Rates Flashcards
A chemical reaction only happens when…
the reactant particles collide with enough energy
The amount of energy the particles need to react is called?
Activation Energy
What is collision frequency?
How often the particles collide with each other
What is percentage success?
The percentage of collisions that have enough energy
What 2 factors affect the collision frequency of rate?
Solid surface area
Solution concentration
What to factors affect the percentage success of rate?
Temperature
Catylists
What is the equation for rate?
Rate = collision frequency x percentage success
How does increasing the concentration/pressure increase rate?
There are more particles per unit volume
So collision frequency is higher
So there are more successful collisions per unit time
How do you increase concentration?
Dissolving more solute particles
How can you increase pressure?
Making the reaction vessel smaller
What experiment is used to demonstrate the effect of concentration?
Reacting thiosulphate solution with hydrochloric acid
How can you increase the surface area?
Cutting or grinding up the solid
What experiment is used to demonstrate the effect of surface area on rate?
Calcium carbonate chips with hydrochloric acid
Describe the relationship between rate and concentration
Rate is directly proportional to concentration
(straight line passing through graph)
How does increasing surface area increase rate?
More solid is exposed to the other particles
So collision frequency is higher
So there are more successful collisions per unit time
Relating to surface area and rate - what happens in a graph?
It is steep at the start however the amount of reactants hasn’t changed so its final area on the graph won’t be different to when the solid isn’t cut up.
How does increasing temperature increase rate?
The particles have more kinetic energy
So the percentage of collisions with enough energy is higher
So there are more successful collisions per unit time
What experiment is used to demonstrate the effect of temperature?
Reacting magnesium with hydrochloric acid (BY HEATING)
Describe the relationship of temperature and rate on a graph?
Its not a straight line because rate isn’t proportional to temperature
It doesn’t go through origin because rate isn’t 0 at 0 degrees
What are catalysts?
Substances which increase rate and remain chemically unchanged
How do catalysts increase rate?
They provide an alternative route with a lower activation energy
So the percentage of collisions with enough energy is higher
So there are more successful collision per unit time
What experiment is used to demonstrate the effect of catalysts?
The decomposition of hydrogen peroxide which is catalysed by manganese oxide (black solid)
Describe the relationship of catalysts and rate on graphs
More effective catalysts increase rate more effectively = steeper line through graph
Why would all lines eventually flatten out in the same total volume, on a catalyst rate graph?
The initial amounts of reactants would stay the same
