Book 2 - Rates, Salts and Electrolysis Flashcards
What is the rate of reaction?
The speed of a chemical reaction.
How do you work out the rate of a reaction?
Amount of reactant used/Time
Or
Amount of product formed/Time
The rate of a chemical reaction can be … Or …
Very fast or very very slow.
Give an example of a very fast chemical reaction.
An explosion
Give an example of a very slow chemical reaction.
Rusting
What is collision theory?
For a chemical reaction to occur, the reacting particles must collide with each other.
Does every collision produce a reaction?
No
What does the rate of collision theory depend on? Name 2 things
- The frequency of collisions between particles
- The energy with which the particles collide
For a collision to be successful, the colliding particles must have the necessary what?
Activation Energy (Symbol Ea)
What is the activation energy?
The minimum energy needed to start a reaction.
For a reaction to start what is needed as well as the activation energy?
The particles need to collide with the correct orientation.
What happens if the number of successful collisions between the reactants increases?
The reaction will speed up.
What factors will affect the rate of a reaction?
- Surface area of a solid reactant
- Concentration of a solution
- Temperature
- Light
- Catalyst
- Pressure of a gas
What can a graph show about the rate of a reaction?
- Reaction is fast at the start because there is a large number of particles reacting
- Reaction slows down because there are less reactant particles than at the beginning
- It stops because all the reactant particles had been used up.
How can the rate of reaction be measured?
Measuring the rate of reaction means measuring the change in the amount of a reactant or the amount of a product.
How can the rate of reaction be calculated from a graph?
Rate of reaction = y/x
What is the Maxwell-Boltzmann theory?
They analysed the distribution of energies of molecules in a sample of a gas. They found that the molecules don’t all have the same energy. They found that some molecules had more energy than others.
How does increasing the temperature affect the reaction rate?
At a higher temperature it increases the amount of molecules with activation energy because there are more successful collisions per second. Which means that the rate of reaction increases.
What will a graph look like after the temperature has been increased for reaction times?
The graphs peak will move to the right.
What is a catalyst?
A catalyst increases the rate without being used up or changed chemically.
What does a catalyst do?
A catalyst provides and alternative route with a lower activation energy.
Overall what is the effect of a catalyst?
Therefore with a catalyst there are more molecules with energy, causing more successful collisions per second. So the rate of reaction increases.
If there is a lot of water and little solute, what is the solution?
Dilute
If there is a large amount of solute in a small amount of water, what is the solution?
Concentrated
What is a solute?
A substance that is dissolved in a liquid to make a solution.
Why do reaction rates increase as the concentration increases?
Before two particles react, they must meet. This is more likely to happen in a concentrated solution than in a dilute one because there more particles are in the same volume which increases the frequency of collisions.
Why does a higher pressure increase reaction rates?
The same number of particles are squeezed into a smaller volume, meaning the closer the particles are together the higher the chance they have of colliding.
Why does increased surface area, increase the rate of the reaction?
A larger surface area increases the frequency of collisions between reactants. E.g When a block of a substance is reacted with a liquid, only the particles exposed at the surface of the block can react whereas if the substance were to be powdered the surface area increases dramatically as all those particles are able to react, increasing the rate of the reaction.
What is an enthalpy change?
The energy change which occurs in a chemical reaction. It the symbol 🔼H and its units are kJmol-1
What is an exothermic reaction?
Energy in the form of heat is given out to the surroundings.
What does an exothermic reaction result in?
An increase in temperature.
Is the sign positive or negative after an exothermic reaction?
Negative
For an exothermic reaction, do you have to put more energy in or do you get more energy out?
You get more energy out when new bonds form in the products than you had to put in to break the bonds in the reactants.
Name four types of reactions that are examples of exothermic reactions.
- Combustion reactions
- Neutralisation reactions
- Redox reactions
- Hydration of anhydrous salts
