Phy Chapter 8 Heat Capacity Caltec S.3

CHAPTER TWO HEAT CAPACITY Heat: The term heat is used to describe the energy transferred through the heating process. Its unit is joules Heat capacity The heat capacity of a substance is the quantity of heat required to rise its temperature by 1°C or 1K. Its symbol is C and its unit is Joule per degree Celsius (J/°C) or Joule per Kelvin (J/K) Heat capacity = mass x specific heat capacity In symbols: C = mc Specific heat capacity Specific heat capacity is the quantity of heat required to raise the temperature of 1kg by 1°C or 1K. Its symbol is c. Its unit is joule per kilogram degree Celsius (J/Kg°C) or joule per kilogram Kelvin (J/KgK) or (JKg-1 K-1). When the temperature of a substance rises; heat gained =mass × specific heat capacity × temperature rises, In symbols: Qgained = m.c (θ2 - θ1) = m.c.θ Where temperature rises (θ) is (θ2 – θ1) , final temperature minus initial temperature. Example-1: Find the amount of heat required to raise the temperature of 2kg of iron from 20°C to 70°C (specific heat capacity of iron is 460J/kg°C) Solution: Mass, m = 2kg Initial temperature , θ1 = 20°C Final temperature, θ2 = 70°C Temperature rises, θ = θ2 – θ1 70 - 20 = 50°C Specific heat capacity of iron ,c = 460J/kg°C Heat gained, Q = ? Q gained = m.c. θ = 2x460x50 46000 joules Hence, the amount of heat required is 46000 joules. Calorimeter and method of mixtures The term calorimeter means the science of heat measurements and any piece of apparatus with which heat measurements may be made is called a calorimeter. In this method hot substances are mixed with cold substances until they reach the same temperature. Assuming that no heat is lost to the …