Sol: Heat can be energy transferred across the boundary of a system because of temperature difference between system and surrounding. The heat is transferred by the processes such as conduction, convection and radiation. The main characteristics of heat are:
1. Heat flows from a system at a higher temperature to a system at a lower temperature.
2. The heat exists only during transfer into or out of system.
3. Heat is positive when it flows into system and negative when it flows out of system.
4. Heat is generally a path function.
5. It is not property of system as it does not represent an exact differential dQ. It is thus represented as Q.
Heat required to raise temperature of a body or system, Q = mc (T2 - T1) Here, m = mass, kg
T1, T2 = Temperatures in °C or K. c = specific heat, kJ/kg-K.
Specific heat for gases is the specific heat at constant pressure (Cp) and constant volume (cv) Also; mc = thermal or heat capacity, kJ.
mc = water equivalent, kg.