Chap 11 Thermal Properties of Matter Flashcards
What is internal energy?
Particles in a solid, held together by strong interatomic or intermolecular bonds, vibrate about fixed positions. The total energy of the particles is called internal energy.
Describe the kinetic component of internal energy?
The kinetic component of internal energy is due to the vibration of the particles. It is directly proportional to temperature and in liquids and gases, the kinetic energy is due to their movement instead of vibrations.
Describe the potential component of internal energy?
Potential component of internal energy is due to the stretching and compressing of the interatomic or intermolecular bonds as particles vibrate. Additionally, the amount of energy stored is dependent on the force between the particles and the distance between the particles.
Define heat capacity.
Heat capacity is the amount of thermal energy required to raise the temperature of a body by 1 K (or 1 Degrees Celsuis)
Define specific heat capacity.
Specific heat capacity is defined as the amount of thermal energy required to raise the temperature of 1kg (unit mass) of a substance by 1K (or by 1 Degrees Celsius).
What is melting point?
The definite temperature at which the change of state from solid to liquid occurs.
What is solidification?
It the change of state from liquid to solid at a temperature equal to its melting point.
What is freezing?
Freezing occurs at a constant temperature. During the change of state, there is no change in temperature even though thermal energy is lost to the surroundings. When liquids molecules come together and solidify, intermolecular bonds are formed. Thermal energy is released during the formation of bonds, hence there is no change in temperature.
How does a liquid boil?
Thermal energy supplied to the liquid but with no rise in temperature. This thermal energy is used to do work to separate the molecules and also to push back on the surrounding atmosphere. As a result, the molecules become further apart with negligible intermolecular forces of attraction. This causes the change of state from liquid to gas.
Define the specific latent heat of fusion.
The specific latent heat of fusion of a solid is the amount of thermal energy required to change 1 kg of the solid to liquid, or vice versa, without a change in temperature.
Define the specific latent heat of vaporisation.
Specific latent heat of vaporisation of a substance is the thermal energy required to change 1 kg of it from liquid to vapour, or vice versa, without any change in temperature.
How does evaporation occur?
Molecules of liquids are always moving randomly at different speeds. These molecules can absorb thermal energy from the surroundings. At the liquid surface, molecules which are more energetic and can overcome the downward attractive forces of other molecules escape into the atmosphere. The slower-moving molecules left behind are cooler as temperature is proportional to the average kinetic energy of the molecules.
How does the temperature of the liquid affect the rate of evaporation?
Raising the temperature of liquid will increase the rate of evaporation. This is because a warmer liquid means a greater number of energetic molecules at the surface layer. Hence, more molecules are energetic enough to escape from the surface.
How does the humidity of the surrounding air affect the rate of evaporation.
Humidity is the measure of how much water vapour there is in the air. The higher the amount of water vapour, the higher the humidity. Hence, evaporation decreases with increasing humidity.
How does the surface area of the liquid affect the rate of evaporation?
The rate of evaporation increases when there is more exposed surface area of the liquid. This is because evaporation only takes place at the exposed surface of a liquid and hence larger exposed surface allows more molecules to escape.
