S.3 HEAT NOTES 2020.pdf

TOPIC: HEAT General Objective: The Learner should be able to; • Quantity heat energy in terms of specific heat capacity and latent heat capacity. • Understand the effect heat on solids and liquids. SUB-TOPIC: QUANTITY OF HEAT SPECIFIC OBJECTIVES The Learner should be able to; • Define heat. • Define heat capacity and specific heat capacity. • Describe an experiment to determine specific heat capacity by method of mixtures. • Solving numerical problems. Examples 1. How much heat energy is given out when a piece of metal of mass 4kg and specific heat capacity 460 Jkg −1K−1 cools from 680C to 600C. (14720J) 2. Calculate the amount of heat required to raise the of 500g of salt from −50C to 150C. (S.H.C of the salt solution = 4000 Jkg −1K−1) (Ans: 40000J) Example A metal block with a heat capacity of 9000 JK−1 is heated from 100C to 500C. Calculate the quantity of heat absorbed. (360kJ) Specific Heat Capacity C = Q (Tf −Ti) This is the amount of heat required to raise the temperature of a substance of mass of 1kg by 1 K. The SI unit is Jkg −1K−1 Q = mc∆T Q = mc(Tf −Ti) S.3 HEAT NOTES 2019 1 HEAT CAPACITY AND CHANGE OF STATE HEAT It is that energy which flows from one body to another due to a temperature difference between them. It is that form of energy whose loss or gain leads to a temperature change. The SI unit of heat is a Joule (J) HEAT CAPACITY This is the quantity of heat required to raise the temperature of a given body by 1K. Its unit is JK−1. Q = C∆T Q = C(Tf −Ti) c = Q