Question

Which of the following is spontaneous at SATP? O H2(g)—2H(9) O Hg(1)—-Hg(9) O N2(g)+2O2(g)+9 kJ—N204(9) O CO2(s)-CO2(g)

Answer 1

Answer: Option (a) is the correct answer.

Explanation:

A spontaneous reaction is defined as the reaction which occurs in the given set of conditions without any disturbance from any other source.

A spontaneous reaction leads to an increase in the entropy of the system. This means that degree of randomness increases in a spontaneous reaction.

For example, $H_{2}(g) \rightarrow 2H(g)$

Here, 1 mole of hydrogen is giving 2 moles of hydrogen. This means that degree of randomness is increasing on the product side due to increase in number of moles.

Hence, there will also be increase in entropy.

Whereas in the reaction, $CO_{2}(s) \rightarrow CO_{2}(g)$ here number of moles remain the same. Hence, the reaction is not spontaneous.

Thus, we can conclude that the reaction $H_{2}(g) \rightarrow 2H(g)$ is spontaneous at STP.