Question

Consider a bimolecular reaction in the gas phase. Which one of the following changes in conditions will not cause an increase in the rate of the reaction? a. Increase the volume at constant temperature. b. Increase the temperature at constant volume c. Add a catalyst d. All of the above will increase the rate of reaction

Short answer

Increasing the volume at constant temperature will not increase the reaction rate.

Step-by-step solution

Understanding Bimolecular Reactions

Bimolecular reactions involve two reactant molecules colliding to form a product. The rate of these reactions can be influenced by factors such as concentration, temperature, and the presence of a catalyst.

Analyzing Increase in Volume at Constant Temperature

If the volume of the reaction container is increased while the temperature remains constant, the concentration of the gases decreases. Since the rate of reaction for bimolecular processes depends on the concentration of the reactants (more collisions occur at higher concentrations), this change will typically decrease the rate of reaction.

Examining Increase in Temperature at Constant Volume

Increasing temperature leads to an increase in the kinetic energy of the molecules, causing more frequent and energetic collisions, which typically increases the rate of a bimolecular reaction, even when the volume is kept constant.

Effect of Adding a Catalyst

A catalyst provides an alternative pathway with a lower activation energy for the reaction to occur. This typically increases the rate of the reaction, as more reactant collisions will have enough energy to surpass the activation energy barrier.

Conclusion on Rate Changes

Given the options, increasing the volume at constant temperature will not increase the rate of a bimolecular reaction, as it leads to a decrease in concentration and therefore fewer collisions between reactant molecules.

Key concepts

Bimolecular Reactions

Bimolecular reactions occur when two reactant molecules collide and interact to form a product. In chemistry, such reactions are fundamental because they offer insights into how molecules transform during reactions. For a bimolecular reaction to successfully occur, the colliding molecules must possess sufficient energy and be oriented correctly during the collision.

• Collisions must be effective, meaning not every collision results in a reaction. The feasibility of a reaction depends on the kinetic energy during the collision and the proper orientation of molecules.
• The reaction rate is tied to the frequency of these effective collisions.
• Factors like concentration and temperature greatly influence how often these effective collisions happen.

Understanding bimolecular reactions helps in grasping how reaction conditions can be manipulated for desired outcomes.

Rate of Reaction

The rate of a reaction describes how quickly reactants are converted to products. In the context of bimolecular reactions, the rate is directly linked to the concentration of the reactants:

• Higher concentration means more molecules are available to collide, which usually increases the rate of reaction. This is because the likelihood of two molecules colliding is greater when there are more molecules present.
• The rate can also be influenced by factors including temperature and the presence of a catalyst. Both can significantly affect how fast or slow a reaction proceeds.
• In bimolecular reactions, the rate of reaction is generally proportional to the product of the concentrations of the two reactants.

By understanding the rate, scientists can determine how quickly a reaction can be expected to proceed under certain conditions.

Effects of Temperature

Temperature plays a crucial role in reaction kinetics. When the temperature of a reaction increases, the molecules involved gain more kinetic energy. This increase in kinetic energy has several effects on the reaction rate:

• Molecules move faster and collide more often, which increases the frequency and energy of collisions.
• These more energetic collisions increase the chance that the molecules will have enough energy to overcome the activation energy barrier necessary for a reaction to occur.
• An increase in temperature typically results in a higher reaction rate because more collisions lead to more successful reactions.

Adjusting temperature is a common way to control the speed of reactions, although it must be managed carefully to ensure desirable outcomes.

Catalysts in Reactions

Catalysts are substances that speed up chemical reactions without being consumed in the process. They achieve this by providing an alternative pathway for the reaction with a lower activation energy. Here's how they function:

• By lowering the activation energy, catalysts allow more reactant molecules to have enough energy to undergo the transformation into products.
• They do not alter the equilibrium of a reaction but enable the system to reach equilibrium faster.
• Different types of catalysts, such as enzymes in biological systems or metals in industrial processes, are used depending on the specific application and reaction.

Catalysts are incredibly important in both industrial and biological processes due to their ability to enhance reaction rates effectively.