Question

On increasing temperature, rate of a reaction increases, because (a) the number of activated molecules increases (b) the number of activated molecules decreases (c) the number of activated molecules becomes zero (d) the activated molecules move with a low speed

Short answer

The correct answer is (a) - increasing temperature results in an increase in the number of activated molecules.

Step-by-step solution

Understanding the concept of activated molecules

Activated molecules are those which carry sufficient energy to cause a chemical reaction. The energy threshold that molecules need to cross for a reaction to occur is known as the activation energy.

Impact of temperature on the number of activated molecules

Higher temperature means more kinetic energy for the molecules of reactants. When kinetic energy of molecules rises, more molecules acquire energy equal to or greater than the activation energy. So, the number of activated molecules increases.

Consideration of the options

Considering the previous two steps and the given options, it can be concluded that increasing the temperature results in an increase in the number of activated molecules. So, the correct answer to this question should be option (a) - the number of activated molecules increases.

Key concepts

Activated Molecules

Understanding how temperature influences chemical reactions is foundational to the study of chemistry. One way it does this is by affecting activated molecules. These are the molecules that have surpassed a certain energy level, allowing them to undergo chemical reactions. Imagine a crowded room where everyone is moving around; a few energetic individuals have the enthusiasm (or in this case, energy) to initiate a new activity. Similarly, not all molecules in a substance are 'activated' or ready to react. They need a specific amount of energy to initiate a reaction.

When the temperature increases, it's like the music's tempo in the room speeding up, giving more people the energy to start dancing. In chemical terms, a higher temperature provides more energy to the molecules, increasing their motion and thus escalating the chances of molecules accumulating enough energy—the activation energy—to become 'activated' and react.

Activation Energy

To understand activation energy, visualize trying to push a car up a hill; the hardest part is getting the car up to the crest of the hill. Once it's there, it can roll down the other side with ease. In a chemical reaction, the 'hill' is the activation energy—the initial energy barrier that must be overcome for reactants to transform into products. It's the 'push' needed to start the reaction.

Every chemical reaction requires a specific amount of activation energy. Temperature comes into play by essentially flattening the hill for more molecules; as the temperature rises, more particles have the kinetic energy needed to reach or surpass the activation energy threshold. Consequently, the reaction rate increases because more molecular 'cars' make it over the 'hill', turning into 'activated molecules' ready to zoom down to product formation.

Kinetic Energy

Now, let's explore the role of kinetic energy. This is the energy that an object—or a molecule—has due to its motion. Think of it as the speed of the particles in a substance. If we revert to the room analogy, we can compare kinetic energy to the speed at which individuals are moving around. If they move faster, they're more likely to bump into each other, increasing the chances for interactions. The same holds for molecules.

As the temperature rises, so does the kinetic energy of the molecules. This is because temperature is a measure of the average kinetic energy of the particles in a substance. With more kinetic energy, molecules move faster and collisions between them become more frequent and more forceful. These high-energy collisions can then lead to a greater number of successful collisions where the activation energy is achieved, thereby facilitating the chemical reaction and enhancing the reaction rate.