Heat:

Heat (symbol: Q) is energy. It is the total amount of energy (both kinetic and potential) possessed by the molecules in a piece of matter. Heat is measured in Joules.

Temperature:

Temperature (symbol: T) is not energy. It relates to the average (kinetic) energy of microscopic motions of a single particle in the system per degree of freedom. It is measured in Kelvin (K), Celsius (°C), or Fahrenheit (°F).

Explanation:

Heat is the total energy of molecular motion in a substance while the temperature is a measure of the average of the molecular motion in a substance. Heat energy depends on the speed of the particles, the number of particles (the size or mass), and the type of particles in an object. Temperature does not depend on the size or type of object. For example, the temperature of a small cup of water might be the same as the temperature of a large tub of water. But the tub of water has more heat because it has more water and thus more total thermal energy.

Note:  Temperature is not energy, but a measure of it. Heat is energy.

DO YOU KNOW?

The crocus flower is a natural thermometer. It opens when the temperature is precisely 23°C and closes when the temperature drops.

Mini Exercise

1. Which of the following substances have a greater average kinetic energy of its molecules at 10°C?

(a)  steel    (b) copper         (c)   water       (d)   mercury

 Ans:   At 10°C water molecules have greater kinetic energy. Due to lesser intermolecular forces as compared to steel, copper, and mercury.

2. Every thermometer makes use of some property of a material that varies with temperature. Name the property used in:

(a) strip thermometers (b) mercury thermometers

(a) strip thermometers:

              Liquid-crystal thermometers use liquid crystals that change color in response to temperature changes. A mixture of liquid crystals is enclosed in separate partitions. Numbers on the partitions indicate temperatures according to the amount of heat present.

(b) Mercury thermometers:

Mercury thermometers are based on the fact that materials (in this case, the liquid mercury) expand when heated.

Mercury has boiling point and less specific heat.

Note:  Due to these properties’ mercury is used in mercury thermometers. Since it is opaque, it is easy to see the capillary.