Question

What is the condition for a chemical reaction to be non-spontaneous:
A. $E_{cell}^ \circ$is positive
B. $\Delta {G^ \circ }$ is negative
C. Reaction quotient, $Q < K$
D. ${E_{cell}}$ is negative

Answer 1

First read about the spontaneous and nonspontaneous reactions.
Spontaneous reaction: Those reactions which are capable to proceed in a given direction without taking the help of any outside source of energy.
Non-Spontaneous reaction: Those reactions which are not capable of proceeding in a given direction by themselves. They need the help of any outside source of energy.

Complete step by step answer:
Exothermic reactions: Those reactions which release heat and energy on completion or during the reaction are known as exothermic reactions.
Endothermic reactions: Those reactions which require heat and energy for completion are known as endothermic reactions.
Enthalpy: Total heat present in the thermodynamic system where the pressure is constant.
Entropy: It is defined as a disorder in the thermodynamic system. It is also defined as $\Delta S = \dfrac{{\Delta Q}}{T}$ where $Q$ is heat and $T$ is the temperature.
Now, we will talk about spontaneous and nonspontaneous reactions.
Spontaneous reaction: Those reactions which are capable to proceed in a given direction without taking the help of any outside source of energy. Favourable conditions for a reaction to be spontaneous are that there should be decrease in enthalpy and increase in entropy of the system. A spontaneous reaction is that who favours the formation of a product in a given set of conditions. For example: Bon fire which is exothermic in nature(i.e. it releases heat and light during reaction), many reactions which occur in laboratories are also examples of spontaneous reactions as they yield products under specific conditions.
Non-Spontaneous reaction: Those reactions which are not capable of proceeding in a given direction by themselves. They need the help of any outside source of energy. Favourable conditions for a reaction to be nonspontaneous are that the reaction should be endothermic or there should decrease in entropy and also both can happen. A non-spontaneous reaction is one who does not favour the formation of a product in a given set of conditions. For example: ${N_2} + {O_2} \to 2NO$ is a highly endothermic reaction but there is positive entropy change.
Hence for the reaction to be non-spontaneous ${E_{cell}}$ should be negative.

So, the correct answer is Option D .

Note:
Read the question carefully like what the question demands. If he is demanding for spontaneous or nonspontaneous. You must know the concept of $Q$and $K$ as there is disbalance like if $Q < K$ then there is a forward shift in the reaction and if $Q > K$ then there is a backward shift in the reaction and for $Q = K$ there is no reaction.