Problem 34 - A Complete Resource Book in Chemistry for JEE Main

Question

According to the collision theory of reaction rates, an increase of the temperature at which the reaction oc curs will inturn increase the rate of the reaction. This caused due to (a) greater number of molecules are having the activation energy (threshold energy) (b) greater velocity of reaction molecules (c) greater number of collisions (d) none of these

Step-by-Step Solution

Answer

The correct answer is (a): greater number of molecules having the activation energy.

Step 1: Understanding Collision Theory

Collision theory states that chemical reactions occur when reactant molecules or atoms collide with enough energy, known as activation energy, to undergo a change. For a reaction to occur, these collisions must be effective, meaning they have sufficient energy and the correct orientation.

Step 2: Effect of Temperature on Reaction Rate

According to collision theory, increasing the temperature increases the kinetic energy of molecules. When molecules have greater kinetic energy, they move faster.

Step 3: Impact of Temperature on Activation Energy

As temperature increases, more molecules have kinetic energy equal to or greater than the activation energy required for a reaction. This results in a higher fraction of molecules being capable of successfully colliding and reacting.

Step 4: Effect on Number of Collisions

Higher temperatures lead to a greater number of molecular collisions because molecules move more quickly and collide more often. However, not all collisions result in a reaction; only those with sufficient energy and proper orientation count.

Step 5: Analyzing the Provided Options

The options given relate to how temperature increase impacts reaction rates: (a) relates to more molecules having activation energy, (b) discusses greater velocity of molecules, (c) concerns more collisions, and (d) states none of these. All of these factors (a, b, and c) are correct effects of increased temperature on reaction rate.

Step 6: Selecting the Correct Answer

While all options can be associated with increased temperature, the primary cause of increased reaction rate due to temperature is (a) more molecules having the activation energy needed for successful collisions. This connects directly to the main principle of collision theory.

Key Concepts

Activation Energy

Activation energy is a fundamental concept in chemistry that explains why not all molecular collisions lead to a reaction. This energy is the minimum amount required for molecules to collide and successfully form a product.
Imagine it as a hurdle that reactant molecules must overcome to transform into products.

• For a reaction to occur, the molecules must hit each other with energy equal to or greater than this activation energy.
• If they don't have enough energy, no reaction will occur.
• This energy requirement ensures that molecules only react under the right conditions.

Understanding this helps explain why certain reactions require a catalyst or need heat to proceed. Catalysts work by lowering the activation energy, making it easier for more molecules to achieve it, thus increasing the reaction rate.

Reaction Rates

The rate of a reaction refers to how quickly reactants are transformed into products. It's a crucial aspect for understanding chemical processes, especially in industries.

• A fast reaction rate means products form rapidly.
• A slow reaction rate indicates a longer time for product formation.
• The speed of a reaction depends on multiple factors, including concentration, surface area, and temperature.

In collision theory, the reaction rate is influenced by how often and how effectively molecules collide. More frequent and effective collisions lead to higher reaction rates. Reactants must not only collide but collide with the right orientation and energy.

Effect of Temperature on Reactions

Temperature plays a significant role in influencing the rate of chemical reactions. As the temperature increases, so does the kinetic energy of the molecules. This increase in kinetic energy has important effects:

• Molecules move faster, leading to more collisions per unit of time.
• More molecules are able to overcome the activation energy barrier.
• Collisions are more energetic, increasing the chances of a reaction.

As a result, reactions tend to speed up as temperature rises. This concept is vital in fields like chemistry and biology, where controlling reaction speed can be crucial, such as in enzymatic processes or industrial synthesis.

Molecular Collisions

In the realm of chemical reactions, molecular collisions are the driving force. They determine whether a reaction will occur and at what rate. Here’s how collisions play a role in reaction dynamics:

• Collisions must be effective: They need proper orientation and sufficient energy.
• Even if molecules collide, without the right conditions, no reaction will happen.
• The more frequent these effective collisions are, the faster the reaction rate.

Understanding molecular collisions helps you visualize how reactions occur at the molecular level and how factors like temperature and catalysts can alter these events. It’s like ensuring dancers in a ballet hit their marks perfectly to create a stunning performance.