Atoms combine to form molecules. These molecules combine to make up a substance. The molecules in a substance are always in a state of random motion.
The kinetic energy due to random motion of molecules of a substance is known as its heat energy. Thus, each body possesses heat energy in the form of its internal kinetic energy.
Temperature and heat are two very different concepts.
The average internal kinetic energy of the molecules of a substance makes up the temperature of that substance. When external heat is applied to a body, its random molecular motion increases, which results in an increase in the aggregate internal kinetic energy of its molecules and thus its temperature increases.
Temperature is not an additive quantity whereas heat is.
The units of heat are joule (J) like all other forms of energy and also calorie, (Cal).
One calorie is defined as the amount of heat energy required to raise the temperature of 1g of water through 1 degree Celsius.
Specific Heat Capacity:
Different substances require different amounts of heat energy to raise their temperature by 1 degree Celsius. For example, a unit mass of water requires 1 calorie of heat to raise its temperature by 1 degree Celsius. A unit mass of copper requires 0.385 calorie heat energy to raise its temperature by the same amount and a unit mass of Iron requires 0.444 calorie heat energy for the same.
This amount of heat energy required to raise the temperature of a unit mass of a substance through 1 degree Celsius is called its Specific Heat Capacity.
Specific heat capacity is thus different for different substances, and it depends not on the mass, but on the nature of material of the substance.
Usually good conductors have a low specific heat capacity while bad conductors have a high specific heat capacity.
High Specific Heat Capacity of Water:
Water has a very high specific heat capacity of around 4.2 J. This high specific heat capacity has lots of natural consequences as well as applications in our daily life.
Some applications of high specific heat capacity of water are-
- Hot Water Bottles are used for Fomentation: Owing to its high specific heat capacity, water absorbs a lot of heat energy to raise its temperature, and it retains this heat energy for a longer period of time. Water is thus used in hot bottles as it provides heat for fomentation for a longer period of time unlike any other substance.
- Water is used as an Effective Coolant: By allowing water to flow in pipes around heated parts of machines like automobiles, excess heat is removed from such parts and overheating is prevented. Water is effective in this case because water takes up more heat energy without undergoing much rise in temperature.
- All Plants and Animals have High Content of Water in Their Bodies: All organisms are made of 80-90% of water because water maintains their body temperature during all seasons due to its high specific heat capacity.
- In cold countries, wine and juice bottles are kept in water as it acts as a heat reservoir and keeps them from freezing in the cold weather.
- Farmers fill their fields with water to protect the crops from frost.
- The high specific heat capacity of water is the reason that the climate near the seashore is always moderate and never extreme.