[PHY] Chapter 11 - Thermal Properties

DARRELL ER (COPYRIGHTED) © TOPIC 11: THERMAL PROPERTIES DARRELL ER (COPYRIGHTED) ©

CHAPTER ANALYSIS THE ABOUT TIME EXAM WEIGHTAGE DARRELL ER (COPYRIGHTED) ©

INTERNAL ENERGY INTERNAL KINETIC ENERGY INTERNAL POTENTAL ENERGY KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

INTERNAL ENERGY OF A SYSTEM The internal energy of a system is the sum of its internal kinetic energy & internal potential energy. The hot coffee has a higher temperature, but not more internal energy. Although the iceberg has less internal energy per mass due to its lower temperature and being in solid state, its enormously greater mass gives it a greater total energy than that in the small cup of coffee. DARRELL ER (COPYRIGHTED) ©

THERMAL PROPERTY HEAT CAPACITY SPECIFIC HEAT CAPACITY KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

UNDERSTANDING HEAT CAPACITY When thermal energy is supplied to a body, the body will undergo an increase in internal energy. The internal kinetic energy will increase, hence the temperature will rise. The amount of energy needed to increase the temperature of the entire body by 1°C is known as heat capacity. The amount of energy needed to increase the temperature of 1kg of the body by 1°C is known as specific heat capacity. IMAGINE THIS You studied too late and you suddenly have a craving for nice shin ramen. You take out the pot and start to boil the water and the water increases from a room temperature of 28°C to 100°C. The heat supplied to the pot is used to increase the temperature of the water. How much thermal energy, Q, will be needed? That depends on the specific heat capacity of water & the mass of water. Q = mcΔθ Q = Thermal energy m = mass c = specific heat capacity Δθ = change in temperature Heat Capacity Specific Heat Capacity Definition Amount of thermal energy required to raise the temperature of the body by 1°C or 1K, without any change in state. Amount of thermal energy required to raise the temperature of a unit mass of a substance by 1°C or 1K, without any change in state. Equation Q = CΔθ Q = mcΔθ SI unit J K-1or J (°C) -1 J kg-1K-1or J (kg °C) -1 Heat capacity and specific heat capacity are related as such: C = mc Heat capacity = mass x specific heat capacity DARRELL ER (COPYRIGHTED) ©

CHANGE IN STATE LATENT HEAT OF FUSION LATENT HEAT OF VAPORISATION EVAPORATION & BOILING KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

MELTING Energy is absorbed to overcome the attractive forces holding the particles together. The amount of energy needed to allow a change in state from solid to liquid is known as latent heat of fusion. FREEZING Energy is released as molecules lose their molecular potential energy and are pulled closer. The amount of energy released during a change in state from liquid to solid is known as latent heat of fusion. BOILING Energy is absorbed to overcome the attractive forces & separate the molecules to be far apart. The amount of energy needed to allow a change in state from liquid to gas is known as latent heat of vaporisation. CONDENSATION Energy is released as molecules lose their molecular potential energy and are pulled closer. The amount of energy released during a change in state from gas to liquid is known as latent heat of vaporisation. CHANGE IN STATE DARRELL ER (COPYRIGHTED) ©

CHANGE IN STATE Latent heat of vaporisation Specific latent heat of vaporisation Definition Amount of thermal energy needed to change a substance from liquid to gas without any change in temperature. Amount of thermal energy needed to change a unit mass of a substance from liquid to gas without any change in temperature. Equation Q = mlv SI unit J J kg-1 Latent heat of fusion Specific latent heat of fusion Definition Amount of thermal energy needed to change a substance from solid to liquid without any change in temperature. Amount of thermal energy needed to change a unit mass of a substance from solid to liquid without any change in temperature. Equation Q = mlf SI unit J J kg -1 The concept is pretty much the same as heat capacity. Heat capacity is to increase temperature. (change in internal KE) Latent heat is to change state. (change in internal PE) DARRELL ER (COPYRIGHTED) ©

CHANGE IN STATE TAKE NOTE! Latent heat of vaporisation is always greater than latent heat of fusion. The bond breaking from liquid state to gaseous state requires a large amount of thermal energy as the intermolecular bonds has to be completely broken to allow the particles to be far apart. Furthermore, as liquid becomes a gas, the increase in volume is more substantial and a huge amount of energy is needed to push the atmospheric pressure away to expand in volume. short time frame, less thermal energy needed longer time frame, more thermal energy supplied DARRELL ER (COPYRIGHTED) ©