37: Factors Affecting the Rate of Reaction Flashcards
(20 cards)
State 5 factors affecting the rate of a chemical reaction.
- Concentration of reactants
- Surface area of solid reactants
- Gas pressure
- Temperature of reaction mixture
- Presence of catalyst
What is the definition of catalyst?
A catalyst is a substance that can change the rate of reaction but remains chemically unchanged at the end of the reaction.
What are two types of catalysts?
Positive catalysts, which speeds up a reaction, and negative catalysts, which slow down a reaction.
What are the conditions for an effective collision between two reactant particles?
- The particle collide with the correct orientation.
- The particles collide with sufficient energy for bonds to break / sufficient energy to overcome the activation energy requirement.
State two possibilities for ineffective collision between two reactant particles.
- Incorrect orientation
- Correct orientation, but with insufficient energy
Explain why increasing the concentration of a reactant increases the rate of reaction with reference to collision theory.
The increase in concentration of reactant means there are more reactant particles per unit volume. These particles are more crowded and collide more often with other reactant particles. The chance of collision increases, so there will be more effective collisions in a unit volume per unit time. Hence the rate of reaction increases.
Explain why increasing the gas pressure of a gaseous reactant at constant temperature increases the rate of reaction with reference to collision theory.
The increase in pressure of reactant at constant temperature means there are more reactant particles per unit volume. These particles are more crowded and collide more often with other reactant particles. The chance of collision increases, so there will be more effective collisions in a unit volume per unit time. Hence the rate of reaction increases.
Explain why increasing the surface area of a solid reactant increases the rate of reaction with reference to collision theory.
The increase in surface area of the reactant means there is a larger surface area over which collisions can occur. The particles collide more often with other reactant particles, so there will be more effective collisions in a unit volume per unit time. Hence the rate of reaction increases.
Explain why increasing the temperature of the reaction mixture increases the rate of reaction with reference to collision theory.
As temperature is increased, reactant particles gain kinetic energy and move faster on average. A larger fraction of the colliding particles now have enough kinetic energy to overcome the activation energy and result in a reaction. In addition, the particles also travel a greater distance per unit time, resulting in more collisions between particles.
Due to these two reasons, the total number of effective collisions in a unit volume per unit time increases, hence the rate of reaction increases.
What is the main reason of increase of rate of reaction when the temperature of the reaction mixture is increased?
It is mainly due to an increase in the fraction of colliding particles with kinetic energy equal to or greater than the activation energy.
Explain why adding a positive catalyst to the reaction mixture increases the rate of reaction with reference to collision theory.
A positive catalyst provides an alternative reaction pathway of lower activation energy. Lowering the activation energy increases the fraction of molecules with enough energy to react, so there are more effective collisions in a unit volume per unit time. Hence the rate of reaction increases.
Name 5 chemical processes that require catalysts.
- Haber process (manufacturing of ammonia)
- Contact process (manufacturing of sulphuric acid)
- Production of nitric acid
- Turning oil into fats in the production of margarine
- Hydrogenation of alkenes
Name the catalysts in the Haber process.
Iron powder
Name the catalysts in the Contact process.
Vanadium(V) oxide
Name the catalysts in the production of nitric acid.
Platinum and rhodium
Name the catalysts in turning oils to fats.
nickel
Name the catalysts in hydrogenation of alkenes.
Platinum or nickel
State and explain three common physical forms of catalysts.
Catalysts are often in the forms of powders, pellets, or gauzes. These forms give them the biggest possible surface area, making them more effective as the reactions they catalyse often involve gases reacting on their surfaces.
What is the chemical nature of enzymes?
They are large protein molecules.
State one applications of enzymes in industry.
Biological laundry detergent contains enzymes and is used to remove biological stains caused by sweat, blood and foods.
