### Related Formula
U = n C_v T$U = n C_v T$
where
C_v = fracf2 R$C_v = \frac{f}{2} R$ and
f$f$ is the degree of freedom.
### Core Logic
Argon (Ar) is monatomic
implies f_1 = 3 implies C_v_1 = frac3R2$\implies f_1 = 3 \implies C_{v_1} = \frac{3R}{2}$.
Oxygen (
O_2$O_2$) is diatomic
implies f_2 = 5$\implies f_2 = 5$ (neglecting vibrational modes)
implies C_v_2 = frac5R2$\implies C_{v_2} = \frac{5R}{2}$.
Total internal energy U = U_1 + U_2 = n_1 C_v_1 T + n_2 C_v_2 T$U = U_1 + U_2 = n_1 C_{v_1} T + n_2 C_{v_2} T$.
### Step 1: Compute Total Energy
U = 8 times left(frac3R2right) T + 6 times left(frac5R2right) T$$U = 8 \times \left(\frac{3R}{2}\right) T + 6 \times \left(\frac{5R}{2}\right) T$$
U = 4(3RT) + 3(5RT)$$U = 4(3RT) + 3(5RT)$$
U = 12RT + 15RT$U = 12RT + 15RT$
U = 27 RT$U = 27 RT$
### Pattern Recognition
Internal energy is strictly additive. Immediately map Monatomic
to 3/2$\to 3/2$ and Diatomic
to 5/2$\to 5/2$. Plug linearly:
8(1.5) + 6(2.5) = 12 + 15 = 27$8(1.5) + 6(2.5) = 12 + 15 = 27$.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Physics: Kinetic Theory of Gases
Class 11 Physics: Thermodynamics