Question

What temperature scale must always be used when working gas law problems?
Options-
A.Celsius scale
B.Kelvin scale
C.Rankine scale
D.Fahrenheit scale

Answer 1

A relative scale can only be used in relative calculations where the units in which the temperature is measured becomes insignificant as one has to make simple comparisons. But gas laws involve a significant use of the magnitude of temperature and therefore an absolute scale of measuring temperatures is preferred.

Complete answer:
The gas law problems deal with the relationship between the physical variables like temperature, pressure and volume associated with ideal or non-ideal gases. The gas laws also involve the use of the universal gas constant $R$ which always involves temperature measured in the Kelvin scale.
The Celsius and Fahrenheit scale are relative scales that have positive, zero as well as negative values of temperature. The negative values associated with these scales can lead to calculation errors as the value of volume and pressure of any gas cannot be negative at any point of time.
The Kelvin scale is a scale that measures the absolute value of temperatures associated with gases. This temperature scale can also be used to consider factors like kinetic energy of the gaseous particles. In fact, zero kelvin temperature is said to be achieved only when the motion of gaseous particles ceases completely and they have zero thermal energy (but it is hypothetical as at such low temperatures no substance remains in the gaseous phase).

Thus, the Kelvin scale is always used while working gas laws and option B is the correct option.

Note:
The Rankine scale is also an absolute scale of temperature measurement with only positive values and therefore a temperature with magnitude zero on this scale would be an absolute zero temperature but it has a limited use only in thermodynamics and is not used when working with the gas laws.