10 — Thermal properties of matter Flashcards
Name heat capacity formula and its SI unit
C (J/d.c.) (heat capacity) = Q (J) (change in internal energy by energy transfer)/ theta (K) (change in tempt)
Latent heat of fusion formula
Lf (J) (latent heat of fusion)=lf (J/kg) (specific latent heat of fusion) x m (kg) (mass)
Internal energy
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.
Heat capacity
Heat capacity C of an object is the change of its internal energy per unit change in its tempt
(It depends on mass & material.)
Total potential energy
Total potential energy depends on
1. Intermolecular forces
2. Spaces betw intermolecular forces of attraction
Specific heat capacity
Specific heat capacity c of a material is the change of its internal energy per unit mass for each unit change in its tempt
Latent heat
Latent heat L is the energy released or absorbed to change the state of a substance, at constant tempt
(-> depends on mass.)
Latent heat of fusion
Latent heat of fusion Lf is the amount of energy transferred to change a substance betw the solid & liquid state, at constant tempt.
Specific latent heat of fusion
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.
Latent heat of vaporisation
Latent heat of vaporisation Lv is the amount of energy transferred to change a substance betw the liquid and gaseous state, at constant tempt.
Specific latent heat of vaporisation
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.
Gain/loss in heat
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
Change in state
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.
Capacity of body depends on
- no. Of particles -> ^, ^ energy can store
- Strength of intermolecular forces -> ^ strength, ^ energy can store (solids & liquids > gas)(non-metals >metals)
Evaporation
- Evaporation of water from x occurs.
- Faster particles at surface hv enuf energy to break away from the other liquid particles to escape into air.
- Particles left behind hv lower spd and ave k.e. Thus tempt decreases
- Since tempt decreases w lower ave. K.e., tempt difference leads to transfer of energy from surroundings to the liquid
Factors that affect evaporation
- Pressure
- Humidity
- Boiling point of liquid
(^, rate of e decreases) - Exposed surface area of liquid
- Temperature
- Wind spd
(^, rate of e increases)
Difference betw boiling and evaporation
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
Why is water often used as the circulating liquid in central heating systems ^ cooling liquid in car engines?
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
Which object has a higher heat capacity? Explain. (answ formula)
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.
Explain when specific heat capacity of water is 4.2kJ/kg K
4.2 kJ of thermal energy is required to change 1kg of water by 1K.
Explain when specific latent heat of fusion of ice is 334kJ/kg
334kJ of energy is needed to change 1kg of the substance betw the solid and liquid state without a change in tempt
Tempt drop for hotter obj = tempt rise for colder obj. Explain your views.
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.
Explain why a jet of steam is more dangerous than same mass of boiling water
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.
Comparison of specific heat capacity of substance
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.
Heat capacity affecting conductivity of heat of obj
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.
What is the purpose of the control apparatus in a joulemeter melting ice experiment.
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.
Explain why the ice used in experiment should be crushed and melting.
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.
Heating curve.
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 ^
Energy of liquid decreases as it turns solid. Explain via molecules.
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.
Explain how condensation of steam causes internal energy of _ to rise and state effect on molecules of _
Steam condenses -> some of energy in internal store transferred to _ by conduction -> _ gains energy in internal store -> molecules move faster n more frequent
Explain why the specific latent heat of vaporisation of water is much higher than the specific heat capacity of water
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]
