Name: Class: Date: Unit 11 THERMAL PROPETIES OF MATTER 82465685 calvinkongphysics@yahoo.com NOTES O-LEVELS REQUIREMENT Candidates should be able to: 1. describe a rise in temperature of a body in terms of an increase in its internal energy (random thermal energy) Sub-topic 9.1C 2. define the terms heat capacity and specific heat capacity 11.1 3. recall and apply the relationship thermal energy = mass x specific heat capacity x change in temperature to new situations or to solve related problems 11.1 4. describe melting/solidification and boiling/condensation as processes of energy transfer without a change in temperature 11.2 5. explain the difference between boiling and evaporation 11.4 6. define the terms latent heat and specific latent heat 11.3 7. recall and apply the relationship thermal energy = mass x specific latent heat to new situations or to solve related problems 11.3 8. explain latent heat in terms of molecular behaviour 11.3 9. sketch and interpret a cooling curve 11.3 Page 1
Content neatly organised so that students can do mental compartmentalisation easily NOTES CONTENT AND ORGANISATION Sub-topic Components 11.1 Heat Capacity (A) Heat Capacity (B) Specific Heat Capacity 11.2 Change of States of Matter (C) Melting and Boiling (D) Freezing (Solidification) and Condensation 11.3 Latent Heat (E) Latent Heat of Fusion (F) Latent Heat of Vapourisation 11.4 Evaporation (G) Explaining Evaporation in Terms of Particles (H) The Cooling Effect of Evaporation (I) Factors affecting the Rate of Evaporation (J) Applications of Evaporation Page 2 8246-5685
11.1 Heat Capacity Internal Energy (Revisit) INTERNAL ENERGY Kinetic Energy Potential Energy Temperature Inter-particle Spacing (A) Heat Capacity The heat capacity, C, of an object is the amount of energy Q, required to raise the temperature of an object by 1 o C or 1 K. where Q = thermal energy absorbed or given out (J) C = heat capacity (JK -1 or J o C -1 ) = change in temperature (K or o C) *Note that 1 Degree Celsius = 1 Kelvin SI Unit: Joules per Kelvin (....) Other common Unit: Joules per Degree Celsius (....) Example 1 John heats up a beaker of pure water. What is the heat capacity of this sample of water if 1260 J of thermal energy is required to raise its temperature by 3 o C? Page 3
(B)Specific Heat Capacity The specific heat capacity, c, of an object is the amount of thermal energy, Q, required to raise the temperature of a unit mass of an object by 1 o C or 1 K. Where c = specific heat capacity (Jkg -1 K -1 or Jkg -1 o C -1 ) C = heat capacity (JK -1 or J o C -1 ) Q = thermal energy absorbed or given out (J) m = mass (kg) = change in temperature (K or o C) SI Unit: Joules per Kilogram per Kelvin (....) Other common Unit: Joules per Kilogram per degree Celsius (....) Example 2 When 211.2 J of thermal energy is transferred to a 12 g sample of pure aluminium, the temperature rises from 15 o C to 35 o C. Calculate the specific heat capacity of aluminium. By rearranging the terms, we have the following useful expression for thermal energy: Example 3 What is the amount of thermal energy required to raise the temperature of a 2 kg mass of copper from 403 K to 453 K? Given that specific heat capacity of copper is 400 Jkg -1 K -1. Page 4 8246-5685
Example 4 (Transfer of Thermal Energy from one body to another, resulting in Thermal Equilibrium) A copper block of mass 400 g is heated using a Bunsen burner. It is then transferred into 200 g of water initially at 30 o C. The final temperature of the mixture is 50 o C. What is the initial temperature of the copper block? Given specific heat capacity of copper is 390 Jkg -1 K -1 ; water is 4200 Jkg -1 k -1. Questions that involved Common Physics Situations are labelled for students easy consolidation. Example 5 (Transfer of Thermal Energy from one body to another, resulting in Thermal Equilibrium) A 50 J s -1 immersion heater is used to heat a beaker containing 300 g of ethanol. The mass of the beaker is 60 g and the initial temperature of the ethanol is 30 C. What is the final temperature of the ethanol after the immersion heater has been kept switched on for 10 minutes? Given specific heat capacity of ethanol is 2500 Jkg -1 K -1 ; glass is 650 Jkg -1 K -1. Page 5
Exercise Questions 1. The heat capacity of a piece of copper is 200 J C -1. What is the amount of thermal energy required to raise its temperature from 30 C to 100 C? Exercise Questions (Basic and Intermediate) after every 1-2 concepts taught 2. When a piece of iron is cooled from 70 C to 40 C, the heat given out is 690 J. (a) What is the heat capacity of the piece of iron? (b) Given that the mass of the iron is 50 g, calculate the specific heat capacity. 3. What is the amount of thermal energy required to raise the temperature of 2 kg of copper from 230 K to 280 K given that the specific heat capacity of copper is 400 J kg -1 K -1? 4. 0.5 kg of orange juice at 30 C is placed in a refrigerator which can remove heat at an average rate of 20 Js -1. How long will it take to cool the orange juice to 5 C? (Assume that the specific heat capacity of orange juice is 4200 J kg -1 C -1 ) Only Section 11.1 - Heat Capacity is shown in this sample Page 6 8246-5685