Engineering
Chemistry
First Law and Various Process
Question

A system contains 1 mol of a monoatomic ideal gas. Now 1 mol of a diatomic nonreacting ideal gas is added into the system at constant volume and temperature. Due to addition of diatomic gas, choose the incorrect statement, regarding the new system.

Internal energy of the system remains constant.

Pressure of the system will increase.

Enthalpy of system will increase

Adiabatic coefficient (γ = CP/CV) of the system will decrease.

JEE Advance
College PredictorLive

Know your College Admission Chances Based on your Rank/Percentile, Category and Home State.

Get your JEE Main Personalised Report with Top Predicted Colleges in JoSA

Solution

Initially, 1 mol monoatomic gas (CV = 3R/2, CP = 5R/2, γ = 5/3). After adding 1 mol diatomic gas (CV = 5R/2, CP = 7R/2, γ = 7/5) at constant T and V, the system has 2 mol total.

The average γ for the mixture is between 1.4 and 1.67, so it decreases. Enthalpy H = nCPT increases as total n and average CP increase. Pressure P = nRT/V doubles, so it increases. Internal energy U = nCVT; while T is constant, total n and average CV increase, so U increases, it does not remain constant.

Final Answer: Internal energy of the system remains constant.