Chemistry MCQs for NEET — Practice Questions with Answers

The NCERT text mentions: 'The dynamic nature of chemical equilibrium can be demonstrated in the synthesis of ammonia by Haber’s process... In order to understand the dynamic nature of the reaction, synthesis of ammonia is carried out with exactly the same starting conditions (of partial pressure and temperature) but using $ ext{D}_2$ (deuterium) in place of $ ext{H}_2$ ... This is not feasible in a school laboratory. However this concept can be easily comprehended by performing the following activity.' And from the summary 'When the number of molecules leaving the liquid to vapour equals the number of molecules returning to the liquid from vapour, equilibrium is said to be attained and is dynamic in nature.' The example of using $ ext{D}_2$ in Haber's process and the suggested activity using colored water (where transfer continues even after levels are constant) both point to continuous microscopic activity, even when macroscopic properties are constant. Directly, 'The dynamic nature of chemical equilibrium can be demonstrated by the use of radioactive isotopes.' is mentioned in the 'Dynamic Equilibrium – A Student’s Activity' section.

The NCERT text states: 'The equilibrium equation is also known as the law of mass action because in the early days of chemistry, concentration was called “active mass”.' It refers specifically to the equilibrium constant expression ($K_c = ext{[C]}^c ext{[D]}^d/ ext{[A]}^a ext{[B]}^b$).

The NCERT text clearly states: 'When the rates of the forward and reverse reactions become equal, the concentrations of the reactants and the products remain constant. This is the stage of chemical equilibrium.'

The NCERT summary states: 'Catalyst does not effect the equilibrium composition of a reaction mixture but increases the rate of chemical reaction by making available a new lower energy pathway for conversion of reactants to products and vice-versa.' Temperature, pressure, and concentration all influence the equilibrium position according to Le Chatelier's principle.

The NCERT text states: 'When the rates of the forward and reverse reactions become equal, the concentrations of the reactants and the products remain constant. This is the stage of chemical equilibrium.'

The NCERT text states under '6.8.1 Effect of Concentration Change': 'The concentration stress of an added reactant/product is relieved by net reaction in the direction that consumes the added substance.' This means the system will shift to counteract the change, i.e., consume the added substance.

The NCERT text uses this as an example of solid-liquid equilibrium: 'Ice and water kept in a perfectly insulated thermos flask (no exchange of heat between its contents and the surroundings) at $273 ext{K}$ and the atmospheric pressure are in equilibrium state and the system shows interesting characteristic features. We observe that the mass of ice and water do not change with time and the temperature remains constant. However, the equilibrium is not static.'

Under '6.1.5 General Characteristics of Equilibria Involving Physical Processes', point (i) states: 'Equilibrium is possible only in a closed system at a given temperature.'

The NCERT text states: 'Similarly, the reaction can reach the state of equilibrium even if we start with only C and D; that is, no A and B being present initially, as the equilibrium can be reached from either direction.'

The NCERT text states: 'The mixture of reactants and products in the equilibrium state is called an equilibrium mixture.'