10 — Thermal properties of matter

Question 1

Name heat capacity formula and its SI unit

Answer 1

C (J/d.c.) (heat capacity) = Q (J) (change in internal energy by energy transfer)/ theta (K) (change in tempt)

Question 2

Latent heat of fusion formula

Answer 2

Lf (J) (latent heat of fusion)=lf (J/kg) (specific latent heat of fusion) x m (kg) (mass)

Question 3

Internal energy

Answer 3

Internal energy is an energy store that is made up of the total kinetic energy associated w the random motion of the particles n the total potential energy betw the particles in the system.

Question 4

Heat capacity

Answer 4

Heat capacity C of an object is the change of its internal energy per unit change in its tempt

(It depends on mass & material.)

Question 5

Total potential energy

Answer 5

Total potential energy depends on
1. Intermolecular forces
2. Spaces betw intermolecular forces of attraction

Question 6

Specific heat capacity

Answer 6

Specific heat capacity c of a material is the change of its internal energy per unit mass for each unit change in its tempt

Question 7

Latent heat

Answer 7

Latent heat L is the energy released or absorbed to change the state of a substance, at constant tempt

(-> depends on mass.)

Question 8

Latent heat of fusion

Answer 8

Latent heat of fusion Lf is the amount of energy transferred to change a substance betw the solid & liquid state, at constant tempt.

Question 9

Specific latent heat of fusion

Answer 9

Specific latent heat of fusion lf is the amount of energy transferred per unit mass of a substance to change betw the solid and liquid state, at constant tempt.

Question 10

Latent heat of vaporisation

Answer 10

Latent heat of vaporisation Lv is the amount of energy transferred to change a substance betw the liquid and gaseous state, at constant tempt.

Question 11

Specific latent heat of vaporisation

Answer 11

Specific latent heat of vaporisation lv is the amount of energy transferred per unit mass of a substance to change it betw the liquid and gaseous states, at constant tempt.

Question 12

Gain/loss in heat

Answer 12

Ke: during heating/cooling, energy transferred to/out of substances -> particles move faster/slower -> ^ in ke/ decrease in ke

Tempt ^/decreases with ^/decrease in average k.e.

PE: potential energy of particles ^/decreases with average separation of particles

Question 13

Change in state

Answer 13

During melting & boiling/ condensation & solidification, energy transferred to/out of substances -> work done against attractive intermolecular forces of attraction betw particles to break intermolecular bonds of molecules -> ave. Separation of particles ^/decreases -> potential energy of particles ^/decreases. However, ave. Ke & tempt remains constant.

Question 14

Capacity of body depends on

Answer 14

1. no. Of particles -> ^, ^ energy can store
2. Strength of intermolecular forces -> ^ strength, ^ energy can store (solids & liquids > gas)(non-metals >metals)

Question 15

Evaporation

Answer 15

1. Evaporation of water from x occurs.
2. Faster particles at surface hv enuf energy to break away from the other liquid particles to escape into air.
3. Particles left behind hv lower spd and ave k.e. Thus tempt decreases
4. Since tempt decreases w lower ave. K.e., tempt difference leads to transfer of energy from surroundings to the liquid

Question 16

Factors that affect evaporation

Answer 16

1. Pressure
2. Humidity
3. Boiling point of liquid
   (^, rate of e decreases)
4. Exposed surface area of liquid
5. Temperature
6. Wind spd
   (^, rate of e increases)

Question 17

Difference betw boiling and evaporation

Answer 17

B needs heat source,E X heat source

B: vaporisation occurs throughout,
E: only @ surface

B: rate of vaporisation faster, E: slower

B: happens only at boiling point, E: below bp above mp

B: liquid tempt constant, E: decreases

B: bubbles formed, E: no bubbles formed

Question 18

Why is water often used as the circulating liquid in central heating systems ^ cooling liquid in car engines?

Answer 18

Water has a v high specific heat capacity -> needs a lot of energy to warm it up. Once warmed, it can store the energy & establish an efficient cooling/heating system

Question 19

Which object has a higher heat capacity? Explain. (answ formula)

Answer 19

Heat capacity of A = but heat capacity of B =. B has a higher heat capacity because it requires a larger amt of thermal energy to raise its tempt by 1K.

Question 20

Explain when specific heat capacity of water is 4.2kJ/kg K

Answer 20

4.2 kJ of thermal energy is required to change 1kg of water by 1K.

Question 21

Explain when specific latent heat of fusion of ice is 334kJ/kg

Answer 21

334kJ of energy is needed to change 1kg of the substance betw the solid and liquid state without a change in tempt

Question 22

Tempt drop for hotter obj = tempt rise for colder obj. Explain your views.

Answer 22

No. Final tempt will be the same but not their change in tempt, heat released by hotter obj will be absorbed by colder obj but change in tempt will be diff if they hv diff heat capacity.

Question 23

Explain why a jet of steam is more dangerous than same mass of boiling water

Answer 23

Water has a higher specific latent heat of vaporisation compared to its specific heat capacity. Huge amt of latent heat of vaporisation is released when steam condenses, can cause harm.

Question 24

Comparison of specific heat capacity of substance

Answer 24

Substance A in _state has a higher specific heat capacity than B OR in _ state of A.
1. For same amount of heating time, rise in tempt is smaller.
OR
2. Gradient of tempt time graph is less steep -> more energy needed to increase 1 tempt per unit time.

Question 25

Heat capacity affecting conductivity of heat of obj

Answer 25

Since heat capacity of _ is smaller, smaller amt of energy has to be removed from _ than _ to cool the drinks to the same tempt, _is preferred.

Question 26

What is the purpose of the control apparatus in a joulemeter melting ice experiment.

Answer 26

To determine the actual mass of water melted by heater alone by finding out difference in mass of water collected in 2 beakers. Calculated value of specific latent heat of fusion lf will be smaller or greater without control experiment, as mass of melted water is taken to be higher value or smaller value/ some heat energy needed to increase tempt of ice to melting point/lost to surroundings, hence calculated lf will be lower or greater.

Question 27

Explain why the ice used in experiment should be crushed and melting.

Answer 27

Crushed ice increase exposed surface area, ensuring good contact between crushed ice and heater. Melting ice confirms the temperature of ice to be at 0d.c.

Question 28

Heating curve.

Answer 28

Heating: Solid/liquid/gas particles gain heat, vibrate/slide past one another/moves in all direction faster, both ke and pe ^, pe ^ w average separation of particles. Change of state: Pe ^ as work done against intermolecular forces and AVE. Sepa of particles ^

Question 29

Energy of liquid decreases as it turns solid. Explain via molecules.

Answer 29

As the liquid changes to solid, the liquid molecules releases latent heat of fusion, resulting in liquid molecules moving closer together to become more closely packed with stronger intermolecular forces of attraction as average separation between molecules decreases hence potential energy decreases. Thus internal energy of the substance decreases.

Question 30

Explain how condensation of steam causes internal energy of _ to rise and state effect on molecules of _

Answer 30

Steam condenses -> some of energy in internal store transferred to _ by conduction -> _ gains energy in internal store -> molecules move faster n more frequent

Question 31

Explain why the specific latent heat of vaporisation of water is much higher than the specific heat capacity of water

Answer 31

More thermal energy needed to overcome the intermolecular forces of attraction between water molecules [1] Energy needed to overcome external atmospheric pressure to escape into the atmosphere [1]