Rates of reaction

what do you measure to measure the rate of reaction

• How fast the reactants are being used up

• How fast the products are being formed

What’s the equations for average rate of reaction (ror)

Ror = quantity of reactants used / time

Ror= quantity of products formed / time

Why does a reaction start off really fast then slow down

Because at the start there are lots of reactants to be used up and react but when it slows down a reactant is all used up

What is collision theory

In order for particles to react they need to collide with each other with sufficient energy called activation energy

What does the rate at any particular point depend on

1. Amount of energy the particles have → more energy the particles have the more energy they can transfer which means the more likely they are to surpass the sufficient energy

2. Frequency of collisions → more often the particles collide means there would be more successful collisions

What factors effect the rate of reaction

1. Temperature

2. Concentration

3. Surface area

4. Catalysts

How does temperature effect the rate of reaction

• increase in temperature means the particles gain more kinetic energy. This means the particles move faster so there are more frequent, successful collisions. Overall creating a higher rate of reaction

• The particles are also more likely to collide with more energy so more likely to exceed the activation energy

How does concentration / pressure effect the rate of reaction

• refers to how many particles per unit of volume

• Concentration refers to solutions, pressure refers to gases

• When either is increased, this increases the number of particles per unit of volume, making collisions more frequent and increases the rate of reaction

How does surface area effect rate of reaction

• If you increase the surface area, it increases the rate of reaction

• E.g out of a powder, solid block and small chunks, the powder would have the highest surface area : volume ratio so the frequency of collisions would increase and therefore increase the rate of reaction

How dies a catalyst effect rate of reaction

• catalyst = substance that specs up the rate of a reaction without being used up itself

  • lowers the activation energy by providing an alternative pathway

How do you work out the actual rate of reaction at a specific time

• calculate the gradient of a curve

  • go the x axis on the certain time till it touches the graph then draw a tangent

  • Gradient = change in Y/ change in X

What is a reversible reaction

• a reaction I’m which both the falward and backward reactions take place at different rates

  → to start the reactants will be quicker than the products as there are no products to start, after a while this evens out and they will be going at equilibrium (concentration of reactants and products won’t change anymore)

What does it mean if a reaction is at equilibrium

• both the Forward reaction reaction and backward reaction happens at the same time but no overall change in concentrations

  → concentrations are constant but not equal to each other

• You would say the equilibrium lies to the side with the most product (left or right)

• If you heat a equilibrium reaction, it will shift to the right and if you cool it it will shift to the left

What system does the reaction have to be in to reach equilibrium

Closed system

→ so no reactants or products can be lost to the surroundings

What is le chateliers principle

If you change the conditions of a reversible reaction, the position of equilibrium will shift to try and oppose the ch age

What are the 3 factors that effect the rate of reaction

• temperature

• Pressure

• Concentration

If you increase the pressure, what position will equilibrium shift to

The side that has the smaller number of gas particles

If equilibrium tries to change pressure, what state does it only effect

Gaseous state