Question

In a chemical reaction reactants \(\rightleftharpoons\) products is shifted towards the products both by increase of pressure and rise in temperature then the forward reaction is (1) endothermic with \(\Delta n\) positive (2) exothermic with \(\Delta n\) positive (3) exothermic with \(\Delta n\) negative (4) endothermic with \(\Delta n\) negative

Short answer

The forward reaction is endothermic with \(\Delta n\) negative (Option (4)).

Step-by-step solution

- Analyze Temperature Effect

When the reaction shifts towards products with an increase in temperature, it indicates that the forward reaction absorbs heat. Therefore, the reaction is endothermic.

- Analyze Pressure Effect

When the reaction shifts towards products with an increase in pressure, the total number of gas molecules should decrease. Hence, \(\Delta n < 0\) where \(\Delta n\) represents the change in the number of moles of gas.

- Combine Observations

Based on the previous steps, the forward reaction must be endothermic (Step 1) and have a negative \(\Delta n\) (Step 2).

Key concepts

Le Chatelier's Principle

Le Chatelier's Principle helps predict how a chemical reaction will shift when it's disturbed. When conditions like temperature, pressure, or concentration change, the reaction shifts to restore balance. If you increase the temperature in an endothermic reaction (one that absorbs heat), the reaction shifts toward the products to absorb extra heat. If the pressure increases and the number of moles of gas on the reactant side is greater than the product side, the equilibrium will shift toward the products to reduce the pressure. Understanding this principle is crucial for predicting reaction behavior and optimizing chemical processes.

Reaction Dynamics

Reaction dynamics refer to how fast a reaction progresses and changes over time. This field studies the steps that occur from reactants forming products. Two major factors influencing reaction dynamics are temperature and pressure. Temperature affects reaction rates because higher temperatures provide more energy for reactants to overcome activation energy barriers. Pressure, especially in gaseous reactions, changes the reaction rate depending on the number of gaseous molecules involved. Reactions with fewer moles of gas on the product side proceed faster with increased pressure, while those with more moles slow down.

Moles of Gas in Chemical Reactions

The concept of moles of gas is key in understanding chemical reactions and their shifts. A mole is a unit measuring the amount of substance. During a reaction, if the total moles of gas decrease (negative \(\Delta n\)), it indicates more gas molecules are consumed than produced. For example, in the reaction given (reactants \rightleftharpoons products), increasing pressure favors the side with fewer gas molecules. If an increase in pressure moves the reaction toward products, it means \Delta n\ is negative. This concept is also crucial in the context of Le Chatelier's Principle, as it helps predict the direction of the reaction under changing conditions.