Question

The molar specific heat of oxygen at constant pressure $Cp=7.03$ cal/mol and $R=8.31$ J/mol. Heat taken by 5 moles from $10^\circC$ to $20^\circC$ at constant volume is approximately:

• A. 25 cal
• B. 50 cal
• C. 253 cal
• D. 500 cal

Hint:

$Cp - Cᵥ = R$ (in Joules). $1$ cal = $4.18$ J.

Answer 1

The Correct Option is C

Step 1: $Cp$ in J: $7.03 × 4.18 = 29.39$ J/mol·K. $Cᵥ = Cp - R = 29.39 - 8.31 = 21.08$ J/mol·K = $21.08/4.18 = 5.04$ cal/mol·K.

Step 2: Heat = $n Cᵥ Δ T = 5 × 5.04 × 10 = 252$ cal ≈ 253 cal.