5.3 Catalysts and their Role in Reaction Kinetics
In industries, reactions are often carried out at high temperatures to produce products quickly. However, high temperatures can be dangerous and may damage certain chemicals. An alternative way to speed up reactions is to use a catalyst.
A catalyst is a substance that speeds up a chemical reaction without being used up itself. It works by providing an easier pathway for the reaction to happen, which has a lower activation energy. With a lower activation energy, more particles can collide effectively, and the reaction happens faster.
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It's important to note that a catalyst doesn't change the overall energy of the reaction or its outcome. It only makes the reaction happen faster. Catalysts cannot make a reaction occur if it is not already possible based on the reaction's energy changes.
Concept Assessment Exercise 5.1
1. How does the presence of a catalyst alter the activation energy of a reaction?
2. Why is it important for a catalyst to remain unchanged at the end of a reaction?
5.3.1 Physical Parameters that Affect the Rate of Reaction
1. Change in Mass
During a chemical reaction, the mass of the reactants decreases because they are used up, while the mass of the products increases as they are formed.
2. Formation of Gas
In some reactions, a gas is produced. If the gas escapes (in an open system), the total mass of the reaction mixture decreases. In a closed system where gas cannot escape, the pressure increases as more gas is formed because the volume stays the same.
3. Temperature
When the temperature of a reaction increases, the particles move faster, causing them to collide more often. This increase in collision frequency results in a faster reaction rate.
5.3.2 Factors Affecting Rate of Reactions
Several factors influence how fast a reaction happens by changing the number of successful collisions between particles. Some of the important factors are:
1. Concentration of Reactants
The more reactant particles there are in a given space, the more likely they are to collide. This means that increasing the concentration of reactants makes the reaction happen faster.
For example, acid rain damages marble more quickly when the acid is stronger. Two antacid tablets neutralize stomach acid faster than one tablet because there are more reacting particles. Hydrogen and chlorine gases react twice as fast if their concentrations are doubled.