C6 Factors Affecting Rates of Reaction (page 143) Flashcards
The rate of reaction depends on what four things?
1) Temperature
2) The concentration of a solution or a pressure of gas.
3) Surface area - this changes depending on the size of the lumps of a solid.
4) The presence of a catalyst
More collisions increases the rate of reaction, explain this?
All four methods of increasing the rate of a reaction can be explained in terms of increasing the number of successful collisions between the reacting particles
Increasing the Temperature
Increasing the concentration or pressure increases the rate
Increasing the surface area increases the rate
Using a catalyst increases the rate
What happens when the temperature is increased, (what factors affect the rates of reaction)?
When the temperature is increased, the particles all move faster.
If they move faster, they’re going to collide more frequently.
Also the faster they move the more energy they have, so more of the collisions will have enough energy to make the reaction happen.
(see picture on page 143)
If you increase the concentration of pressure, this increases the rate of reaction, why?
If a solution is made more concentrated, it means there are more particles knocking about in the same volume of water (or other solvent).
Similary, when the pressure of a gas is increased, it means that the same number of particles occupies a smaller space.
This makes collisions between the reactant particles more frequent.
(see picture on page 143)
If one of the reactants is a solid, what will happen if you break it up into smaller pieces?
breaking it into smaller pieces will increase its surface area to volume ratio.
This means that for the same volume of the solid, the particles around it will have more area to work on, so there will be collisions more frequently.
A catalyst is a substance that speeds up a reaction without it being used up in the reaction itself, what do this mean?
This means it’s not part of the overall reaction equation.
Different catalysts are needed for different reactions, but they all work by decreasing the activation energy needed for the reaction to occur. They do this by providing an alternative reaction pathway with a lower activation energy.
Enzymes are biological catalysts - they catalyse reactions in living things
(see diagram on page 143)
Catalysts are really useful, why?
they don’t get used up so you can use them over and over again.
For each of the following pairs of reactions, state which one would have a fastest rate (A or B) and why?
a) A: A 2g solid strip of magnesium with water. B: 2 g of powdered magnesium with water
b) A: 2 mol/dm³ HCl with excess ethanoic acid. B: 4 mol/dm³ HCl with excess ethanoic acid
a) B (1 mark) because the powder has a higher surface area to volume ratio than the solid strip (1 mark)
b) B (1 mark) because the 4 mol/dm³ HCl solution is more concentrated than the 1 mol/dm³ solution (1 mark)
