KVPY2019ChemistryStates of Matter
For one mole of a van der Waals' gas, the compressibility factor Z = p V R T at a fixed volume will certainly decrease, if [Given : " a " and " b " are standard parameters for van der Waals' gas]
Options
- A" b " increases and " a " decreases at constant temperature
- B" b " decreases and " a " increases at constant temperature
- Ctemperature increases at constant a n and " b " values
- D" b " increases at constant " a " and temperature
Correct answer
B. " b " decreases and " a " increases at constant temperature
Step-by-step solution
If p 0 and V 0 are used as notation of ideal pressure and ideal volume of a van der Waals' gas, the actual pressure and volume are: p = p 0 - a n 2 V 2 , V = V 0 + n b ∴ As ' ' d ' ' increases, P decreases, 80 p V R T decreases, when temperature is constant. and, as " B ' decreases, V decreases, so p V R T decreases, when temperature is constant. Note option (c) : When temperature increases, p   V also increases and therefore Z would not necessarily decrease.