Thermal Properties of Matter

Why are gaps left between railway rails, why does a lake freeze from the top downwards, and why does a metal spoon in hot tea feel hot? This chapter explains such everyday observations through the thermal properties of matter. It begins by distinguishing temperature, a measure of hotness, from heat, the energy transferred because of a temperature difference. You will study thermometers and the Celsius, Fahrenheit and Kelvin scales, and see how the ideal gas equation leads to the absolute temperature scale. Thermal expansion of solids, liquids and gases is described by the coefficients of linear, area and volume expansion, and the anomalous expansion of water is explained. The chapter introduces specific heat capacity, molar specific heat and the principle of calorimetry, in which heat lost equals heat gained. You will study changes of state, including melting, boiling and sublimation, with latent heat and the effect of pressure on boiling point. Finally, it covers heat transfer by conduction, with thermal conductivity, and by convection and radiation, and ends with Newton's law of cooling.

Detailed Worksheet: Thermal Properties of Matter Section A - Definitions (10 marks) 1. Distinguish between heat and temperature. (2 marks) 2. Convert 40 degrees Celsius to the Fahrenheit scale. (2 marks) 3. State the relation between the coefficients of linear, area and volume expansion. (2 marks) 4. Define specific heat capacity and write its SI unit. (2 marks) 5. Why does a lake freeze from the top? (2 marks) Section B - Calculations and Applications (15 marks) 6. A steel rail is 10 m long at 0 degrees Celsius. Find its increase in length at 40 degrees Celsius. Take alpha = 1.2 x 10^-5 per K. (3 marks) 7. Find the heat needed to raise the temperature of 2 kg of water from 20 to 80 degrees Celsius. Take c = 4186 J/kg K. (3 marks) 8. A glass window of area 1 m^2 and thickness 5 mm separates a room at 20 degrees Celsius from the outside at 5 degrees Celsius. Find the rate of heat flow through it. Take K = 0.8 W/m K. (3 marks) 9. Explain why the boiling point of water rises in a pressure cooker. (3 marks) 10. State Newton's law of cooling and the conditions under which it holds. (3 marks) Section C - Diagrams (10 marks) 11. Draw the temperature-time graph for heating ice at -10 degrees Celsius until it becomes steam, and label the regions. (4 marks) 12. Draw a graph showing the variation of the volume of a fixed mass of water between 0 and 10 degrees Celsius. (3 marks) 13. Draw a diagram showing convection currents in a sea breeze during the day. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. A sphere of 0.047 kg aluminium is placed in boiling water at 100 degrees Celsius and then quickly transferred into a 0.14 kg copper calorimeter containing 0.25 kg of water at 20 degrees Celsius. The final temperature is 23 degrees Celsius. Find the specific heat of aluminium. Take the specific heats of water and copper as 4180 and 386 J/kg K. (5 marks) 15. Find the heat needed to convert 3 kg of ice at -12 degrees Celsius into steam at 100 degrees Celsius. Take specific heats of ice and water as 2100 and 4186 J/kg K, latent heat of fusion 3.35 x 10^5 J/kg and of vaporisation 2.256 x 10^6 J/kg. (5 marks) 16. Explain conduction, convection and radiation with examples, and derive the expression for heat flow H = KA(T1 - T2)/L through a slab. (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Take the specific heat of water as 4186 J/kg K unless stated otherwise. Show units at every step.