Full transcript
0:01hello this is Dr Henna aseel and this is
0:04IGCSE chemistry and today we're talking
0:08about states of matter solids liquids
0:11and gases so let us take a look at the
0:16difference between solid liquid and
0:19gases if we look at how particles are
0:23arranged and the separation between the
0:26particles and the differences in the
0:29movement of the particles so if he's
0:32asking about separation of particles in
0:35a solid remember that particles in a
0:38solid are closely packed and that means
0:42they are touching they're very close to
0:44each other
0:47in liquids the particles are near to
0:51each other so remember that if he says
0:53draw the particles of a liquid some of
0:57them should be touching and some of them
0:59not touching but they are not too far
1:03away and they're not too close to each
1:05other so we say they are near each other
1:07in clusters what about particles in a
1:11gas you should realize that particles in
1:13a gas are far apart please pay attention
1:17what is he asking about if he's asking
1:21about separation then this is what we
1:23should say but if he's asking about
1:25Arrangement how are particles in a solid
1:29arranged you should realize that in a
1:32solid the particles are in regular rows
1:36what about in a liquid we say they are
1:39in random arrangements or sometimes we
1:43say irregular Arrangement but random
1:46Arrangement is a much better one and gas
1:49is also the particles are randomly
1:52emerged
1:53what about movement so please notice is
1:57he asking about Arrangement or movement
1:59if he's saying movement how do particles
2:02in a solid move please do not say they
2:06don't move
2:08all particles move
2:10but the difference is in solids they
2:14vibrate in fixed position the particles
2:17in their position are vibrating for a
2:21liquid the particles move around each
2:25other or sometimes we say they slide
2:28over each other in gases it's fast free
2:33random motion remember that if we're
2:37talking about movement the particles of
2:39a gas move faster than liquids and
2:43solids also if we're talking about
2:46energy
2:47the energy in gases in the particles of
2:51a gas is much higher so the particles
2:54any gas are the ones that have higher
2:57energy
2:58what if we're saying which one is
3:01compressible you know that compressible
3:03means which one can we press the
3:07particles nearer to each other of course
3:10a solid the particles are already
3:12touching each other so they cannot be
3:15pressed anymore so they are not
3:17compressible in liquid we also say that
3:21particles in a liquid are not
3:22compressible but the particles in a gas
3:25originally are far apart so it is
3:29compressible you can press the particles
3:33with Under Pressure the particles will
3:35come nearer to each other
3:38which of these has a fixed volume
3:42of course solids have a fixed volume
3:44what about liquids yes they do they have
3:47a fixed volume because the amount of
3:49water you have in a bottle if you pour
3:52it into a cup it is still the same
3:54volume so it has a fixed volume but what
3:57about gases remember that gases will
4:01fill up any volume
4:04they are present in so if you have
4:06particles in a balloon when the balloon
4:10bursts the gas
4:12spreads
4:14all over into a larger volume so gases
4:18do not have a fixed fault which one has
4:21a fixed shape of course solids have a
4:25fixed shape but the liquid takes the
4:27shape of the container the gas takes the
4:30shape of the container
4:33okay so let's take a look at some of the
4:36questions so this is a question it says
4:38in which of the following are the
4:40particles arranged in a regular pattern
4:44do you remember
4:46we said if we have solid liquids and gas
4:48the one that are arranged in regular
4:51rows is which one it's the solid so the
4:55question is which of these is a solid of
4:58course if he says a gas or a liquid or a
5:00metal you should realize that the metal
5:03is a solid so the particles will be
5:06arranged in regular rows
5:09the diagram shows a cup of tea which row
5:12describes the water particles in the air
5:15above the cup compared with the water
5:19particles in the cup so he's comparing
5:21particles of a liquid to the particles
5:24of a gas so if he's saying what are we
5:30saying about the particles in the air is
5:32it moving faster
5:34yes of course the particles in a gas we
5:37said will move faster what about closer
5:42together will the gas be closer together
5:44no So my answer would be B can you see
5:48that
5:51okay another question says four
5:53statements about the arrangement of
5:54particles are given and the question is
5:58which statements describe the particles
6:01in a solid so we're talking about solid
6:04liquid or gas and he's saying which
6:07statement is correct for a solid so
6:10let's take a look at the statements the
6:12first one says particles are packed in a
6:15regular arrangement in a solid yes
6:20particles are randomly arranged in a
6:24solid no
6:26particles move over each other in a
6:29solid no we said the particles move over
6:32each other in liquid not in a solid
6:34particles vibrate
6:37yes that's how particles move in a solid
6:41so the one that is correct is one and
6:43four one and four means my answer is
6:46B
6:51so this is another kind of questions
6:53he's saying describe the arrangement and
6:56motion of molecules in in what in a gas
7:00how are the particles in a gas arranged
7:04we said in a gas the particles have
7:08random Arrangements what about motion so
7:12if he's asking about Arrangement don't
7:14talk to him about mush a same motion or
7:17movement how do the particles in a gas
7:20move it is a free random motion you
7:24could also say that it is fast random
7:27motion describe the arrangement and
7:29motion of particles in copper sulfate
7:32Crystal now it doesn't matter
7:35copper sulfate or any other compound but
7:38in a crystal that's in a solid so in any
7:41solid the arrangement is regular rows
7:46movement or motion of particles in any
7:49solid vibrates in fixed position
7:54describe the arrangement and motion of
7:56particles in liquid stearic acid
8:00well it doesn't matter what steric acid
8:02is if you don't know what it is all he's
8:05asking about is Arrangement and motion
8:07of particles in any liquid
8:10so in Arrangements in any liquid random
8:13arrangement
8:14motion move around each other or slide
8:18over each other
8:20okay another question in which substance
8:23are the particles furthest apart at room
8:27temperature
8:29well if we look at solids liquids and
8:31gases you know that the ones that are
8:34furthest apart would be the gas so the
8:38question is which of these is a gas you
8:40should know that ethanol is a liquid
8:43methane is a gas
8:46salt and sugar are solids so in which
8:50substance of the particles furthest
8:52apart in the gas which is methyl
8:55at room temperature in which substance
8:58of the particles further support again
9:00what is hydrogen hydrogen is a gas
9:04water is a liquid at room temperature
9:08magnesium is a solid magnesium oxide is
9:12a solid so at room temperature which
9:16substance are the particles furthest
9:18apart that's the one that's a gas and
9:20that is hydrogen
9:23some students are asked to describe
9:25differences between gases and liquids
9:28three of their suggestions are these and
9:31he's saying which suggestions are
9:33correct so basically he wants which of
9:36these statements are correct when we're
9:39comparing gases and liquids so the first
9:43statement says gas molecules are further
9:46apart is that correct or wrong yes if
9:50you look at the particles of a gas
9:51compared to a liquid the gas molecules
9:54are further apart are gas molecules
9:58smaller than a liquid remember if he's
10:02saying molecules are smaller or
10:05molecules or larger no
10:08the molecules do not change their size
10:11when they move from liquid to gas
10:15they remain the same size they don't
10:17become smaller or bigger they just move
10:20further apart now he's saying liquid
10:23molecules vibrate around fixed positions
10:28no we said which ones vibrate the ones
10:31that vibrate are the solid so which
10:33suggestions are correct it's only the
10:35first one so my answer is
10:37hey
10:39which rule describes the spacing and
10:42arrangement of particles in a solid a
10:44liquid and a gas again if we remember
10:47solids liquids and gas first of all for
10:50a solid
10:51my options are they are close together
10:54and randomly arranged or they are close
10:58together and regularly arranged remember
11:01that for a solid they are close together
11:04and regularly arranged So my answer is C
11:08or D
11:09then liquids are what liquids are close
11:13together and randomly arranged and gas
11:16is far apart and randomly arranged So my
11:20answer is
11:23the arrangements of particles and solids
11:25liquids and gases are different which
11:27statement about the molecules in ice
11:30water or steam is correct remember that
11:33ice is the solid form of water
11:37um water at what we call water is the
11:40liquid form and steam is the gas form of
11:44water so which of these statements is
11:47correct he's saying the water molecules
11:49are on average closest together in Steam
11:53no steam is a gas so that's wrong the
11:57water molecules are on average furthest
12:00apart in water
12:03no water is a liquid the molecules of
12:07water should be further apart in the
12:10form of steam or in the form of a gas
12:12the water molecules in Steam have the
12:16second highest average velocity
12:20we said which of these moves faster
12:23velocity means movement
12:26which one moves faster remember the
12:28molecules of a gas
12:30are the fastest so they're not the
12:33second highest they're actually the
12:35highest velocity the water molecules in
12:38ice are able to vibrate yes because ice
12:42is the solid form and we said molecules
12:44in solids vibrate
12:48in which state does one decimeter cubed
12:51of methane contain the most particles
12:56so we have a certain
12:58volume
13:00in which of these will the
13:03this specific volume of one decimeter
13:06cubed have the most particles remember
13:10that if we have the most particles that
13:14means I want the particles to be nearer
13:16to each other so that in that volume I
13:19will have more because as we become
13:22liquid and gas the same volume will have
13:25less molecules so which of these has the
13:30um
13:32more particles remember if I have a gas
13:36at 100 degrees Celsius that is
13:39a higher temperature than gas at room
13:42temperature so actually the one at
13:44higher temperature will have even less
13:47particles the gas temp the gas at room
13:50temperature will have
13:53still more than the high temperature but
13:56the one that will have the most is the
13:59solid So my answer here is d
14:03you should know the pressure of a gas is
14:05due to particles hitting the inner
14:08surface of the container so if I have
14:12particles remember the particles are
14:15constantly moving and they're hitting
14:16each other and they're hitting the walls
14:18of the container now when temperature of
14:21the gas is increased so at higher
14:23temperature the pressure of the gas also
14:26increases this is because when we heat
14:29it the particles gain more kinetic
14:32energy move faster hit the sides of the
14:36container faster and with stronger Force
14:40so when we have particles in a balloon
14:42you know that when the balloon is put in
14:46the Sun for example at high temperature
14:48the particles will start to gain kinetic
14:51energy move faster hit the sides of the
14:54balloon faster and eventually the
14:57balloon becomes larger and it will burst
15:03so let's take a look at this question
15:04which row represents the particles of a
15:07gas colliding most frequently so when
15:11will particles of a gas Collide most
15:15frequently
15:16if we're talking about pressure they
15:18will collide more frequently at high
15:21pressure or at low pressure you should
15:23realize that at higher pressure you're
15:25pressing the particles nearer to each
15:28other so the particles will tend to
15:30collide with each other more so I need
15:33to choose high pressure what about
15:36temperature at high or low we said at
15:39high temperature the particles have more
15:41energy so they're moving faster so they
15:44will collide more frequently so this
15:47happens at high pressure and at high
15:51temperature
15:54let's talk about change of state so if I
15:57have a solid what should I do to the
15:59solid to change it into a liquid I
16:01should heat it so when you heat a solid
16:04or when you leave a piece of ice at high
16:07temperature or at room temperature it
16:10will start to change into a liquid this
16:12change from solid to liquid is called
16:15melting so if we say what is meant by
16:18melting melting is the change of state
16:21from solid to liquid what is meant by
16:25melting point remember we have
16:27melting happens at a specific
16:30temperature
16:31this can be referred to as melting point
16:34or melting temperature so melting point
16:38or melting temperature is the
16:41temperature at which solid changes to
16:44liquid
16:46what if we're changing so from solid to
16:49liquid is melting what if I continue to
16:52heat the liquid and remember we're
16:53heating from solid to liquid I need to
16:55heat it I need to give it heat
16:58so if you remember what exothermic and
17:02endothermic means Endo means the
17:05reaction takes in heat soil I am heating
17:08the solid so this is an endothermic
17:11reaction it becomes liquid I heat the
17:14liquid it becomes a gas now what does
17:16that change of state what do we call it
17:20we call it boiling and this boiling is
17:24the change of state from liquid to gas
17:26but remember that we could also call it
17:30evaporation so you need to distinguish
17:33between boiling and evaporation boiling
17:37is the change of state from liquid to
17:40gas at a fixed temperature remember that
17:43boiling happens at a specific
17:45temperature which we call the boiling
17:48point or the boiling temperature so this
17:51is the temperature at which the liquid
17:54changes into gas
17:56but we can also have evaporation and you
18:00know that evaporation is the change from
18:03liquid to gas also just like boiling but
18:06this happens at any temperature not at a
18:10fixed temperature
18:12and it will occur only on the surface of
18:15the liquid while boiling happens all
18:18over the
18:20okay so heating a solid to liquid this
18:23is melting when liquid changes into a
18:26gas that's boiling what if I cool the
18:30gas so that it becomes a liquid that is
18:34called condensation so if we say what is
18:37meant by condensation it is the change
18:40of state from gas to liquid cooling the
18:43liquid to form a solid that is called
18:46freezing so freezing is the change from
18:49liquid to salt
18:52some substances when they are solid and
18:55we heat them they change directly into
18:58gas this is called sublimation so
19:01sublimation
19:03is the change from solid to gas or gas
19:07to solid without passing through the
19:10liquid state
19:13so if we look at this question the three
19:16states of matter are solid liquid and
19:18gas and he drew solid liquid and gas and
19:21he wants to know what is X Y and Z
19:24please pay attention where is X and
19:27where is y and Warrior Z what is X x is
19:31the arrow going from liquid to gas
19:34change from liquid to gases boiling you
19:38could say evaporation but we usually say
19:41boiling now from gas to Liquid from gas
19:45to liquid that's cooling the gas change
19:48into liquid that is condensation and
19:52from liquid to solid from liquid to
19:55solid that is freezing
19:58what are the processes W X Y and Z in
20:02this diagram again
20:04pay attention to the direction of the
20:06arrows so w is going from what to what
20:11from solid to liquid solid to liquid is
20:14melting So my answer is C or D
20:19what about x what is X x is from liquid
20:24to gas again we said from liquid to gas
20:27that is boiling So my answer is C from
20:32what is y can you see what is y y is
20:36from liquid to solid so that is correct
20:39that's freezing and Z is gas to liquid
20:43and that is condensed
20:46the diagram shows a kettle of boiling
20:49water as the water vapor cools it turns
20:54into droplets of liquid water the change
20:57of state when vapor changes into liquid
21:01this is from what from vapor from gas to
21:07liquid can you see from gas to liquid
21:09that is condensation
21:13the diagram shows how the arrangement of
21:16particles changes when a substance
21:18changes state which change of state is
21:21shown well what does he have he has what
21:24a solid going to gas so that is
21:29sublimation and that is d
21:33diagrams or SNT represent the three
21:37states of matter which change occurs
21:40during freezing what is freezing
21:43freezing is change from liquid to solid
21:48so which one is liquid to solid that is
21:53B
21:54okay
21:57when iodine is heated it turns from
22:00solid to gas what is that called
22:04solid to gas that is sublimation
22:07when liquid ammonia is cooled it turns
22:11into a solid so this is liquid
22:15to solid that is freezing when ice is
22:19heated it turns into water ice is solid
22:23turns into water that's a liquid that's
22:26melting So my answer here is which one
22:31can you see how we're choosing the
22:34answers
22:36okay diagrams of the three states of
22:39matter for carbon dioxide are shown
22:41which two diagrams show the states of
22:44matter
22:44before and after
22:47sublimation what is sublimation
22:50sublimation is from solid to gas so
22:54which of these is solid and which of
22:56these is gas you can see that solid is
22:59three
23:00and gases one where the particles are
23:04very far apart so please notice that he
23:07could rearrange it rearrange the boxes
23:10any way he wants the sublimation is from
23:14solid to gas which of these is solid the
23:16one where the particles are regularly
23:18arranged so that is three
23:21to one where the gas is particles far
23:26apart so that is sublimation
23:29now when he asks what happens during
23:33melting or what happens during boiling
23:36remember for something to melt or to
23:39boil we need to heat it so what is
23:42happening when we heat these particles
23:45if he says what's happening during
23:47melting or what is happening during
23:50boiling well the substance is heated so
23:53what happens particles gain kinetic
23:56energy move faster
23:58overcome the attraction forces between
24:02them and move further apart that's how
24:05we explain what is happening during
24:08melting or during boiling you're heating
24:12the substance so the particles gain
24:14kinetic energy when they gain kinetic
24:17energy they move faster
24:19in that order
24:21and when they move faster then they can
24:24overcome the attraction forces between
24:27them and move further apart
24:31so what happens during condensing or
24:34during freezing of course the liquid is
24:37changing to solid for example so that is
24:40freezing you need to cool it so when a
24:43substance is cooled particles lose
24:45kinetic energy move slower and come
24:49nearer to each other
24:52okay this is how you explain what is
24:55happening so this is a question heating
24:57a liquid causes it to become a vapor
25:00what happens to the molecules of the
25:03liquid during this process so if I'm
25:06heating the liquid and becomes a gas
25:09will the molecules become bigger
25:13again we set the molecules never become
25:17bigger or smaller So my answer is C or D
25:21okay then the molecules will move
25:24further apart if I'm changing from
25:27liquid to gas or to Vapor yes so my
25:31answer is
25:34describe the changes in Arrangement
25:37movement and energy of the particles
25:42when the liquid wax cools to become a
25:46solid so liquid anything
25:49cools to become assault what is the
25:53change in Arrangement movement and
25:56energy of the particles well you should
26:00realize I am cooling the liquid and it
26:03becomes a solid then the particles are
26:06losing kinetic energy so the energy will
26:10be less
26:11in the solid they will move slower so
26:15that is the change in the movement and
26:17they will come closer to each other and
26:20become regular Arrangements in rows when
26:25they become assault so this is how you
26:28explain and please notice that you need
26:31to explain each part of the question
26:34Arrangement movement and energy of the
26:38particle so they lose energy or cooling
26:40it
26:42they lose energy so that's the change in
26:45energy they move slower
26:47and they come closer to each other and
26:50become regular Arrangements in rules
26:53which process causes the greatest
26:56increase in distance
27:00between particles so which one will
27:04cause the particles to move away from
27:07each other
27:09with the biggest distance of course if
27:13we're changing from solid to gas then
27:17the particles have moved away with a
27:20greater increase in distance So my
27:23answer is sublimation
27:26pure water boils at 100 degrees Celsius
27:30what happens to the water particles when
27:34water boils again if I am boiling water
27:39will the particles gain energy or lose
27:43energy we're avoiding it that means
27:46you're heating it you're giving it extra
27:48energy so the particles gain energy and
27:52then they will move from liquid to gas
27:54so will they move further apart or stay
27:58close together well they will move
28:02further apart so during boiling the
28:06particles gain energy and they move
28:09further apart and become a gas
28:14four physical changes are listed in
28:18which changes do the particles move
28:21further apart again which of these will
28:24cause the particles to move further
28:26apart condensation can you see where
28:28condensation is no the particles move
28:31nearer
28:32evaporation evaporation means from
28:36liquid to gas yes they will move further
28:38apart freezing freezing is from liquid
28:42to solid no they're moving nearer
28:45sublimation from solid to gas yes they
28:50move further apart so my answer is two
28:54and four so that is C
28:57are we following all of this okay
29:00in most questions or in some questions
29:03he will give you certain melting point
29:06and certain boiling point and ask you is
29:09the substance a solid or a liquid or a
29:11gas at a certain temperature so for
29:14example if we know that something is
29:16solid at room temperature and remember
29:18room temperature is taken as 20 degrees
29:22Celsius or 25 degrees Celsius this is
29:27what we refer to as room temperature
29:30so if something is a solid at room
29:33temperature
29:34what does that tell you
29:37it tells you that at room temperature it
29:41hasn't melted yet and that means its
29:44melting point is higher than room
29:46temperature and the boiling point is
29:49always higher than the melting point so
29:51if the melting point is high then the
29:53boiling point will be much higher so if
29:57he gives me a substance a for example
30:00whatever and he says the boiling point
30:02is high and the melting point is high
30:04then at room temperature that substance
30:08is assaulted
30:09what if a substance is a liquid at room
30:13temperature that means at room
30:15temperature it has already melted and
30:17that means we have passed the melting
30:19point so the melting point must be low
30:22lower than room temperature
30:24but it hasn't boiled yet so the boiling
30:27point is higher than room temperature so
30:31if something has low melting point high
30:34boiling point then at room temperature
30:37it is a liquid what if something is a
30:40gas at room temperature that means it
30:43has already melted and it has already
30:45boiled so that means at room temperature
30:48we have passed the melting point and the
30:51boiling point and that means that it has
30:53very low melting point and very low
30:56boiling points are we following
30:59okay so let's see this question the
31:02melting points and boiling points of
31:04four substances are shown which
31:07substance is a liquid at a hundred he's
31:11not asking at room temperatures asking
31:13at a hundred now for something to be a
31:16liquid at a hundred what does that mean
31:19we said that means its melting point is
31:22lower than a hundred but its boiling
31:26point is higher than a hundred so which
31:29of these has melting point lower than
31:33100
31:34and boiling point higher than 100
31:38a has very low melting and boiling
31:41points that would make it a gas at a
31:44hundred
31:44uh B has low melting point and its
31:49boiling point is lower than 100 so it
31:52will also be a gas but C it has melting
31:55point flow Boiling Point High that means
31:58it's
32:02okay then the next question says a
32:05compound X has a melting point of 71 and
32:09avoiding point of 375 and that means
32:14that above 71 it's a liquid
32:18until 375 that's the boiling point so
32:22above 375 it's a gas and the question
32:26says which statement is correct
32:30so it's a liquid at 52
32:33at 52 it has not reached the melting
32:37point yet so it has not melted so
32:41actually at 52 it's still a solid now
32:45the next choice says it's a liquid at 69
32:49no it has to be a liquid above
32:5271. so if he says it's a liquid at 75 or
32:56around 80 that is correct So my answer
32:58is C or D
32:59now in order to be a gas it has to be
33:02above
33:04375 so that means my answer is d
33:09the melting point of three related
33:11compounds are these the boiling point of
33:14all these compounds is above a hundred
33:17give the physical state of each acid at
33:21room temperature
33:22first of all we don't care what capric
33:24or formic or palmitic means we have just
33:27have three compounds
33:30and he's given me the melting point of
33:35each of them so capric acid he says the
33:39melting point is 32 so the melting point
33:42of capric acid is 32 and the boiling is
33:48a hundred so all of them above 100 are
33:51gases at 32
33:56if the melting point is 32 that means at
34:00room temperature I have not reached the
34:02melting point and that means it hasn't
34:04melted yet so that means it's a solid
34:07what about formic acid formic acid has a
34:10melting point of eight now that means by
34:13the time we reach room temperature it
34:16has already melted so it's a liquid what
34:19about palmitic acid the melting point of
34:21palmitic acid is 63 and that means at
34:25room temperature it has not melted yet
34:28so it is assault
34:32substance L melts at -7 and is a brown
34:38liquid at room temperature which
34:41temperature is the boiling point of pure
34:44l
34:46so pure first of all means it should
34:49have a specific melting point so B and D
34:54are wrong you cannot boil over a range
34:58unless if there is impurities but a pure
35:01substance should have a fixed boiling
35:03point so the question is is the boiling
35:06point minus 77 or 59 well you should
35:11realize that it melts at -7
35:15and that means its boiling point should
35:19be higher remember that minus 77 is
35:22lower than -7 so it melts at -7 it's a
35:28liquid at room temperature and that
35:30means its boiling point must be higher
35:32than room temperature so that is 59
35:36that's reasonable
35:37then we have a heating curve a heating
35:41curve means I am following the uh change
35:45in solid liquid and gas as I increase
35:48the temperature so if I start with a
35:51solid and I'm heating it that means the
35:54temperature of the solid is increasing
35:56until I reach a certain temperature
35:59which is the melting point now during
36:02melting the temperature does not rise
36:06because the increase in Heat or the
36:09increase in energy is used to change the
36:12solid to liquid so during melting the
36:17temperature does not increase even
36:19though we're still heating the salt
36:21until everything becomes a liquid then
36:25the temperature starts to rise now the
36:28temperature of the liquid will continue
36:30to rise until we reach the boiling point
36:33at that temperature the liquid will
36:37start to boil and the temperature
36:39remains constant during boiling until
36:43everything changes into a gas then the
36:47temperature of the gas will continue to
36:50increase so this is called a heating
36:53curve remember the flat areas in the
36:57curve represent the change of state
37:00whether it's melting or boiling when the
37:04temperature is rising that means you're
37:06heating the solid or the liquid or the
37:09gas now what if I start with a gas and I
37:13cool it now when I cool it the
37:15temperature decreases it will continue
37:17to decrease until we reach
37:20our temperature at which condensation
37:24happens remember that a substance will
37:28condense at the same temperature that it
37:32boiled so if I say the substance has a
37:35certain boiling point it is the same as
37:38the condensation point
37:41so the gas is changing into a liquid
37:45that is during condensation that's the
37:47flat area in the curve until all of it
37:50has become liquid I continue to cool so
37:53the temperature of the liquid will go
37:56down
37:57until we reach what
38:00the freezing point at a temperature it
38:03will start to freeze now while it is
38:07freezing the temperature remains
38:09constant until all of it has become a
38:12solid then the temperature will start to
38:16decrease
38:17please remember the condensation point
38:20is the same as the boiling point the
38:24freezing point is the same as the
38:26melting point so if your substance has a
38:29certain melting temperature or it melts
38:31at a certain temperature it will freeze
38:34at that same temperature
38:37so this question says a solid metal is
38:40heated until it turns to Vapor the graph
38:43shows the temperature of the metal
38:44during this process which part of the
38:48graph shows the melting of a metal a
38:51metal means I'm starting solid so that
38:55means where is the solid the solid is at
38:57a until it starts to melt and that means
39:01it is melting at B remember the flat
39:04area after a solid that's the Melt
39:08the diagram shows a heating curve is X
39:12solid liquid or gas at room temperature
39:15where is room temperature room
39:17temperature is 20 so 20 is between 15
39:21and 80. remember that this graph says
39:24that 15 is the melting point
39:28uh 80 is the boiling point so at 20 it
39:32has already melted it is a liquid
39:35name the change of states which occurs
39:38in D to e remember that it started as a
39:42solid at a
39:44now at C it has become liquid now at D
39:47it is
39:49doing boiling it is changing from liquid
39:53to gas
39:56explain how the curve shows that a pure
39:59sample of compound X was used remember
40:02we said if something is pure it will
40:05have a fixed sharp melting point
40:09and a fixed sharp Boiling Point now what
40:14if it were impure if it were impure then
40:17it will melt over a range so this area B
40:20C or D E will be
40:22a bent line between two temperatures
40:27and it will not have a fixed
40:30melting point or a fixed boiling
40:35okay we're going to stop here now and
40:37next time we're going to continue
40:39talking about diffusion
40:47okay thank you for listening and please
40:50continue listening to the videos we will
40:52be doing all the chapters
40:56according to the new syllabus in the
40:58IGCSE