Thermal Properties of Matter Flashcards
Define internal energy
The internal energy of a body is the total kinetic energy due to the motion of the molecules and the potential energy due to the intermolecular forces in the body.
State what causes a change in internal energy.
The transfer of thermal energy into or out of a body will cause a change in its internal energy.
Changes in either the kinetic or potential energy will cause a change in the internal energy.
Define heat capacity
The heat capacity of a body is the quantity of energy needed to cause its temperature to change by 1 oC. (SI units are J oC-1 or J K-1
State two factors that influence heat capacity.
- Identity of substance
2. Mass of substance in the body
Define specific heat capacity.
The specific heat capacity of a substance is the quantity of energy needed to change the temperature of 1 kg of the substance by 1 oC or 1 K. (Units: J kg-1 oC-1 or J kg-1 K-1)
State the formula that is derived from specific heat capacity.
Q = mcΔθ
Define latent heat
The amount of thermal energy absorbed or by a substance during a change of state, without a change in its temperature. (SI unit: J)
Explain why the temperature remains constant during melting.
Between Q and R, thermal energy is absorbed to break the strong bonds between the particles of the solid ice. Only the total internal potential energy of the particles is increased. Since total internal kinetic energy does not increase, the temperature remains constant during melting.
Explain why the temperature remains constant during boiling.
The average kinetic energy of the molecules increases. From Y to Z, the temperature of the water remains steady at 100°C as it boils and turns into steam. The thermal energy supplied is used to separate the water molecules, as well as provide energy for the molecules to push back on the surroundings to escape into the air.
Define latent heat of fusion
It is the amount of thermal energy required to change a substance from a solid to a liquid (or vice versa) without a change in temperature.
Define latent heat of vaporisation
It is the amount of thermal energy required to change a substance from a liquid to a gas (or vice versa) without a change in temperature.
Define the boiling
Boiling is the change of state from liquid to gaseous state, occurring at a fixed temperature called the boiling point.
Define evaporation
Evaporation is the change of state of a liquid into gaseous state, at any temperature.
Evaporation causes cooling.
State 5 factors that could influence the rate of evaporation
- Temperature
- Humidity of the surroundings
- Surface area
- Pressure
- Nature of liquid
