C8 Flashcards
What is rate of reaction?
A measure of how quickly a reactant is used up, or a product formed.
What are the two things required for a chemical reaction to occur?
- Reactant particles must collide with each other
- The particles must have enough energy for them to react
What is a successful collision?
A collision between reactant particles that has enough energy for a reaction to happen.
What is activation energy?
It is the minimum amount of energy needed for a collision to be successful.
How do you calculate the rate of reaction?
- Quantity of reactant used * time taken
2. Quantity of product formed * time taken
On graphs the gradient of the line is usually equal to…
The rate of reaction.
What are the units for rate usually?
Cm3/s
Cm3/min
Mol/s
If the concentration of a reacting solution or the pressure of a reacting gas is increased what happens to the rate of reaction?
The reactant particles become more crowded so the frequency of collision between the reactant particles increases. Therefore the rate of reaction increases.
What doesnt happen to the particles no matter the conditions?
The mean energy if the particles doesnt change.
The steeper the tangent…
The faster the reaction.
If a large lump is ground into a powder what happens?
Its total volume stays the same
The area of exposed surface increases
The surface area to volume ratio increases
What happens to the rate of reaction if surface area to volume ratio is increased?
More reactant particles are exposed at the surface so the frequency of successful collisions between the particles increases. Therefore increasing rate of reaction.
A faster reaction on a graph will…
Give a steeper line and finish sooner
What happens to the rate of reaction as temperature increases?
The reactant particles move more quickly and the energy of the particles increases, so the frequency and proportion of successful collisions between the particles increases. Therefore the rate of reaction increases.
What is a catalyst?
It is a substance that…
- speeds up the rate of reaction
- does not alter the products of the reaction
- is not chemically changed or used up at the end of the reaction
How do catalysts work?
They provide an alternate pathway that has a lower activation energy than the uncatalysed reaction. This doesnt change the frequancy of collision but it does change the frquency of successful collisions as the particles have greater energy than the activation energy.
What is a reversable reaction?
A chemical reaction where the products of the reaction can react together to produce the original reactants and vice versa.
What may happen to the reaction mixtures reactants and products if the conditions are changed?
Their proportions may be changed.
If a reaction is exothermic in one direction it will be…
Endothermic in the other direction (the same amount of energy is transferred in both forward and reverse reactions).
When will a reversible reaction reach dynamic equilibrium?
When it is in a closed system.
What are the properties of reversible reactions when they reach dynamic equilibrium?
- the forward and backward reactions are still happeningbut they both have the same rate of reaction.
- the concentration of all reacting substances remain constant.
If the forward reaction is exothermic, when temperature increases…. and when temperature decreases…
As temperature increases the amount of product formed decreases
As temperature decreases the amount of product formed increases
If the forward reaction is endothermic, when the temperature increases… and when the temperature decreases…
When the temperature increases the amount of products formed also increases.
When the temperature decreases the amount of products formed also decreases.
What is Le Châtelier’s principle?
Whenever a change is introduced to a system at equilibrium, the position of equilibrium shifts so as to cancel out the change.
