Rates of reaction - 4.3 Flashcards
How does concentration increase the rate?
- Increasing concentration increases rate of reaction
- More particles in the same volume
- More frequent collisions
- More successful collisions per unit time
How does pressure increase the rate?
- increasing pressure increases the rate of reaction
- same number of particles in a smaller - volume
- more frequent collisions
- more successful collisions per unit time
How does temperature increase the rate?
- increasing temperature increases rate of reaction
- the particles have more kinetic energy
- There are more collisions with the required energy
- more successful collisions per unit time
How does surface area increase the rate?
increasing surface area increases the rate of reaction
more of the reactants particles are exposed
more frequent collisions
more frequent collisions per unit time
How does a catalyst increase the rate of reaction?
- Provides an alternate route with lower activation energy
- more successful collisions per unit time
what is a catalyst
a substance that increases the rate of reaction without getting used up
Describe the disappearing cross experiment.
The effect of concentration on rate can be demonstrated by reacting sodium thiosulphate
solution with hydrochloric acid:
Na2S2O3(aq) + 2HCl(aq) → 2NaCl(aq) + S(s) + SO2(g) + H2O(l)
- a solid sulphur is slowly produced
- after a while you can’t see through the mixture any longer
- this is measured by observing a black cross under the mixture
Variables:
- input: the concentration of the Na2S2O3(aq)
- output: the time taken for the cross to disappear
- control:
–> total volume of the solution
–> concentration of HCl(aq)
–> temperature
Rate is calculated from the times taken:
rate (s-1) = 1/ time taken (s)
What do the results from the disappearing cross experiment look like on a graph?
The results are proportional meaning it shows a straight line going through the origin.
Describe the marble chip experiment.
The effect of surface area on rate is usually demonstrated by reacting calcium carbonate (marble) chips with hydrochloric acid:
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
Variables:
* Input: the sizes of the CaCO3(s) chips
* Output: the volume of CO2(g)
* Control:
o Mass of CaCO3(s)
o Volume and concentration of HCl(aq)
o Temperature
what do the results from the marble chip experiment look like on a graph?
Comparing the higher surface area line to the original line:
* higher surface are has a steeper start:
This is because the rate has increased, so the volume of CO2 is increasing faster.
* Same final volume:
This is because the total amounts of reactants hasn’t changed, so eventually the reaction
produces the same amount of CO2
Describe the magnesium and acid experiment.
The effect of temperature on rate can be demonstrated by reacting magnesium with hydrochloric acid:
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
In this reaction, the magnesium disappears.
Variables:
* Input: the temperature of the HCl(aq)
* Output: the time taken for Mg(s) to disappear
* Control:
o Mass and surface area of Mg(s)
o Volume and concentration of HCl(aq)
Rate is then calculated from the times taken:
rate (s-1) = 1/ time taken (s)
What do the results from the magnesium and acid experiment look like on a graph?
It’s not a straight line
This is because rate isn’t proportional to temperature.
It doesn’t go through the origin
This is because rate isn’t zero at 0 degrees C
Describe the hydrogen peroxide experiment.
The effect of a catalyst on rate can be demonstrated using the decomposition of hydrogen peroxide:
2H2O2(aq) → 2H2O(l) + O2(g)
Catalysts are not in the reaction equation because they are unchanged during the reaction.
- the reaction is normally very slow and takes days to finish
- it is catalysed by manganese(IV) oxide which is a black solid
- this causes it to take place in only a a few seconds
Variables:
* Input: which catalyst is being used
* Output: volume of O2(g)
* Control:
o Volume and concentration of H2O2(aq)
o Temperature
o Mass and surface area of catalyst
What do the results from the hydrogen peroxide experiment look like on a graph?
More effective catalysts increase rate more effectively.
This results in a steeper line on the graph.
- the initial amounts of reactants is the same
–> all lines would eventually flatten out at the same total volume of O2
What is catalysed to produce oxygen in the lab?
The MnO2(s)-catalysed decomposition of hydrogen peroxide is used to produce oxygen in the lab
