Question

Listed in the table are forward and reverse rate constants for the reaction $2NO\left(g\right)\rightleftharpoons N_2\left(g\right)+O_2\left(g\right)$.

Temperature (K)	$k_f\left(M^{-1}{s}^{-1}\right)$	$k_r\left(M^{-1}{s}^{-1}\right)$
1400	0.29	$1.1\times {10}^{-6}$
1500	1.3	$1.4\times {10}^{-5}$

Is the reaction endothermic or exothermic?

• A. Exothermic reaction
• B. Endothermic reaction
• C. Can't predict
• D. None of these

Answer 1

The correct option is A Exothermic reaction

At 1400 K,

$K=\frac{K_f}{K_r}=\frac{0.29}{1.1\times {10}^{-6}}=2.64\times {10}^5$

At 1500 K,

$K=\frac{K_f}{K_r}=\frac{1.3}{1.4\times {10}^{-5}}=9.29\times {10}^4$

Thus, with an increase in temperature, the value of the equilibrium constant decreases. Hence, the reaction is exothermic.