Question

The unit of thermal capacity is:
\[\begin{align}
  & \text{A}\text{. }cal/{}^{\circ }C \\
 & \text{B}\text{. }cal/g \\
 & \text{C}\text{. }cal/g\text{ }{}^{\circ }C \\
 & \text{D}\text{. }cal \\
\end{align}\]

Answer 1

Hint: Thermal capacity gives the information of how the matter will act when the substance is heated. Thus clearly it depends on temperature. Hence option B and D can be ruled out. Then the answer is either A or C. Does thermal capacity also depend on mass? If it does then the answer is C, if not then the answer is A.

Complete step by step answer:
Thermal capacity or the heat capacity is an extensive property of the matter; it is the amount of heat required to increase the temperature by $1{}^{\circ }C$ of any material of given mass. Its SI unit is given as $J/K$ or joule per kelvin.
The thermal capacity is a function of pressure and temperature, in other words it depends on the temperature and the pressure applied to the material.
The other units include, joule per degree Celsius $J/{}^{\circ }C$ . Since heat is also measure in terms of calories, it can be written as $cal/{}^{\circ }C$

So, the correct answer is “Option A”.

Additional Information:
Other forms of representing heat capacity are:
1. Molar capacity, where the amount of the substance is given by moles.
2. Volumetric heat capacity, where the heat capacity is measured with respect to volume.
3. Specific heat capacity: where the heat capacity is measured per mass of the sample.

Note: The change in temperature is the same in both kelvin and Celsius scales. i.e. $0{}^{\circ }C=273K$ and $1{}^{\circ }C=274K$ if we take the difference, we will see that the both give the same unit rise in temperature. The conversion of calories per degree to joule per kelvin is often used as is given by$1cal/{}^{\circ }C=4.184J/K$. The unit of thermal capacity or heat capacity is $cal/{}^{\circ }C$ , while the unit of specific heat capacity is \[cal/g\text{ }{}^{\circ }C\]