Chapter 4 - Rates And Energy Flashcards
What are the two reactions for finding the rate of reaction
Rate of reaction=
Amount of reaction used/time
OR
Amount of product formed/time
How can we use a graph of amount of product against time to tell us the rate of the reaction at a given time
By using the gradient of the graph. The steeper the gradient is, the faster the reaction is at the time
What is the collision theory
Theory that states reactions can only happen if particles collide. However particles must collide with enough energy to change into new substances
What is the activation energy
The minimum energy particles need to react
What factors increase the rate of reaction (chance of collisions)
- Temperature
- Concentration of solutions
- Pressure of gases
- Surface area of solids
- Using a catalyst
Why do powders react faster than large pieces of solid
Breaking large pieces of solids into smaller pieces exposes new surfaces and so increases the surface area. This means there are more collision sin the same time. The finer the powder the faster the reaction
What happens when the concentration of a solution is increased
More particles dissolve in the same volume. This means the dissolved particles are closer together and so they collide more often
Why does the rate of a reaction increase when the concentration of a reactant is increased.
The particles collide more frequently
Why does the rate of reactions that have gases as reactants increase
Increasing the pressure of a gas puts more molecules into the same volume, and so they collide more frequently
What do catalysts do to the activation energy
They lower it so that more of the collisions result in a reaction
Give an advantage of a catalyst
It is not used up and is left at the end of the reaction and so can be used over and over again
How are catalysts made effective
By having a large surface area
Why do different reactions need different catalysts
Because catalysts often work with only one type of reaction
What are the benefits of using catalysts in industrial processes
They are economical because they do not need replacing very often. They can reduce the energy and time needed for reactions. This helps to reduce costs and reduce impacts on the environment. Using catalysts will help to conserve resources and reduce pollution
What is a disadvantage of transition metal catalysts
They are toxic and may cause harm if they get into the environment
What are the advantages of enzymes (biological catalysts) replacing more traditional catalysts
They will reduce energy costs even further
What is an exothermic reaction
Reactions that transfer energy to the surroundings. Energy transferred often heats up the surroundings and so the temperature increases
Why is energy transferred when chemical reactions take place
Bonds are broken and made
Examples of exothermic reactions
- Combustion
- Oxidation reactions such as respiration
- Neutralisation reactions involving acids and bases
What is an endothermic reaction
Reaction that takes in energy from the surroundings. Some cause a decrease in temperature and others require a supply of energy
Name two products which use exothermic reactions
Hand warmers & self heating cans
Name a product which uses endothermic reactions
Cold packs
How can the rate be found
By measuring how much of a reactant is used or how much of a product is formed, and the time taken
