Problem 13 - A Complete Resource Book in Chemistry for JEE Main

Question

In what manner will increase of pressure affect the following equation? \(\mathrm{C}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \rightleftharpoons \mathrm{CO}(\mathrm{g})+\mathrm{H}_{2}(\mathrm{~g})\) (a) shift in the reverse direction (b) shift in the forward direction (c) increase in the yield of hydrogen (d) no effect

Step-by-Step Solution

Answer

The reaction will shift in the reverse direction.

Step 1: Analyze the Chemical Equation

Examine the chemical equation: \(\mathrm{C}(\mathrm{s}) + \mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \rightleftharpoons \mathrm{CO}(\mathrm{g}) + \mathrm{H}_{2}(\mathrm{g})\). It has 1 mole of gaseous reactant and 2 moles of gaseous products.

Step 2: Apply Le Chatelier's Principle

Le Chatelier's Principle states that increasing pressure will favor the side with fewer moles of gas. In the given reaction, there is 1 mole of gas on the left and 2 moles on the right.

Step 3: Determine the Direction of Shift

Since increasing pressure will favor the side with fewer moles of gas, the reaction will shift towards the side with fewer moles. Hence, it will shift in the reverse direction.

Key Concepts

Chemical Equilibrium

Chemical equilibrium is a state where the rate of the forward reaction equals the rate of the reverse reaction. In this state, the concentration of reactants and products remains constant over time. It does not mean that the reactions stop; they continue, but since they occur at the same rate, no net change is observed in the concentrations of the substances involved.

In the context of our exercise, the chemical equation, \[\mathrm{C} (\mathrm{s}) + \mathrm{H}_{2} \mathrm{O} (\mathrm{g}) \rightleftharpoons \mathrm{CO} (\mathrm{g}) + \mathrm{H}_{2} (\mathrm{~g})\]is at equilibrium when the rates of formation of water and carbon are equal to the rates of formation of carbon monoxide and hydrogen.

Understanding how equilibrium is achieved in this reaction provides insights into how reactions are balanced in closed systems. Key factors such as concentration, pressure, and temperature can affect this balance, altering the ratios of reactants and products.

Pressure Effect on Reactions

Pressure plays a significant role in reactions, especially in those involving gases, due to its direct impact on the concentration of gaseous reactants and products. Le Chatelier's Principle helps us predict how changes, like pressure, impact the position of equilibrium. It states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change and restore equilibrium.

In our discussed reaction:\[\mathrm{C} (\mathrm{s}) + \mathrm{H}_{2} \mathrm{O} (\mathrm{g}) \rightleftharpoons \mathrm{CO} (\mathrm{g}) + \mathrm{H}_{2} (\mathrm{~g})\]The system will respond to increased pressure by shifting its equilibrium point to minimize the change. Since the left side has 1 mole of gas while the right has 2, increasing pressure favors the reverse reaction, which results in fewer gas molecules. This shift aims to alleviate the pressure increase by forming products that occupy less volume.

Gaseous Reactants and Products

In chemical reactions, especially those involving gases, it's crucial to consider the state and number of molecules. Gaseous reactants and products play an important role in determining how a reaction will proceed under varying conditions like pressure and temperature.

For the reaction \(\mathrm{C} (\mathrm{s}) + \mathrm{H}_{2} \mathrm{O} (\mathrm{g}) \rightleftharpoons \mathrm{CO} (\mathrm{g}) + \mathrm{H}_{2} (\mathrm{~g})\), understanding that \(\mathrm{H}_2\mathrm{O}, \mathrm{CO},\) and \(\mathrm{H}_2\) are gaseous is vital. Their behavior under pressure changes is guided by gas laws. More gas molecules mean more volume, so a system will adjust to reduce pressure by moving to the side with fewer gaseous molecules when pressure is increased.

Therefore, knowing the physical state of each reactant and product helps predict the atmospheric and chemical scenario outcomes when pressure changes, impacting the rate and direction of the reaction.