C6- The Rate And Extent Of Chemical Change- Paper 2 Flashcards
What is meant by the term activation energy?
Activation energy is the minimum amount of energy needed for a reaction.
Give one example of a slow reaction.
Chemical weathering like acid rain to limestone buildings.
Give one example of a moderate speed reaction.
Metal magnesium reacting with an acid.
What is an example of fast reaction.
Burning but explosions are faster
What are the 2 factors in the collision theory?
- The collision frequency (the more collisions there are the faster the reaction it)
- The energy transferred during a collision (particles have to collide with enough energy for the collision to be successful)
How can you find the speed of a reaction?
Recording the amount of reactant used up over time.
What 4 things affect the rate of reaction?
- Temperature
- The concentration of a solution or the pressure of gas
- Surface area
- The presence of a catalyst
How does temperature increase the rate of reaction? (3 marks)
When the temperature is increased, the particles all move faster.
If they’re moving faster, they’re going to collide more frequently.
The faster they move the more energy they have, so more of the collisions will have enough energy to make the reaction happen.
How does the concentration or pressure increase the rate of reaction? (3 marks)
If a solution is made more concentrated, it means there are more particles knocking around in the same volume of solvent.
Similarly, when the pressure of a gas is increased, it means that the same number of particles occupy a smaller space.
This makes collisions between the reactant particles more frequent.
How does surface area affect the rate of reaction?
If one of the reactants is a solid, then breaking it up 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.
What is a catalyst?
A catalyst is a substance that speeds up a reaction, 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.
For each of the following pairs of reactions, state which one would have the fastest rate and why.
1. A: a 2g solid strip of magnesium with water B: 2g of powered magnesium with water
2. A: 2 mol/dm3 HCl with excess ethanoic acid B: 4mol/dm3 HCl with excess ethanoic acid
- B- because the powder has a higher surface area to volume ratio than the solid strip
- B- because the 4mol/dm3 HCl solution is more concentrated than the 2mol/dm3 solution
What is a closed system?
None of the reactants or products can escape and nothing else can get in
What is Le Chatelier’s Principle?
If you change the conditions of a reversible reaction at equilibrium, the system will try to counteract that change.
It can be used to predict the effect of any changes you make to a reaction system.
Exothermic
The outside will get warmer as the reaction is transferring energy to the surrounding.
Endothermic
Takes energy in from the surroundings so the surroundings get cooler
What happens when you decrease the temperature of a reversible reaction?
If you decrease the temp, the equilibrium will move in the exothermic direction to produce more heat. This means you’ll get more products for the exothermic reaction and fewer products for the exothermic reaction.
