What is the rate of a reaction?
Measure of how quickly reactants are used or products are formed
Rate of reaction = mass of reactant used / time
Rate of reaction = mass of product formed / time
Why and how do we measure the volume of a gas for rate of reaction?
If the product is in gas state it is easier to measure its volume than mass
- either use an upturned measuring cyclinder in water
OR
Use a gas syringe :
1) place a reactant in a conical flask connected to a gas syringe (make sure it is at 0)
2) add the other reactant and close the flask with a stopper and start the stop clock
3) with a results table, record the tip, e and volume of the gas at regular time intervals
How to calculate the mean rate of reaction from a graph?
1) calculate the changes in volume and time over the given time interval
2) calculate the mean gradient = change in volume / change in time
What is the collision theory?
Reactions only occur if reactant particles collide with each other and have enough activation energy to react
Why would a reaction not occur even with collisions?
Collision didn’t have enough energy OR collision didn’t occur at the correct angle/orientation
What are the factors that affect rate of reaction?
- temperature
- concentration
- pressure
- SA
- catalysts
How does temperature affect the rate of reaction?
- when you increase the temperature the rate it occurs at increases as particles gain more kinetic energy
- therefore they collide more frequently
- as the particles have more energy a greater proportion would have higher activation energy
- so there are more successful collisions and so a a greater rate of reaction
How can you investigate the affect of temperature on rate?
Reaction between sodium thiosulfate solution and hydrochloric acid
1) in a beaker mix the reactants on top of a white tile with a cross and start a stop clock
2) stop the clock when the cross disappears
3) the longer it takes for the cross to disappear the slower the reaction
4) change the temperatures by heating up one of the solutions before reacting them in a water bath of ice bath
What is the reaction time and what is its relationship with rate of reaction?
Time taken for reaction to occur
Inversely proportional
How does concentration affect rate of reaction?
- When you increase the concentration of a chemical reaction the particles become more crowded than before and so will collide more frequently
- The rate of successful collisions increases and therefore the rate increases
How can you investigate the effect of concentration of the rate of reaction?
Reaction between magnesium ribbon and hydrochloric acid
1) measure the time taken for the piece of magnesium ribbon to be used up
2) change the concentrations of hydrochloric by adding water
3) 1/time to find the rate
How does pressure of gases affect the rate of reaction?
- with increased pressure of a chemical reaction, the rate of reaction increases
- as the particles become crowded than before (less space)
- collide more frequently in a given time
- therefore a greater rate of reaction
How does SA affect rate of reaction?
- with increased SA the surface area to volume ratio increases
- more particles available for collisions
- collisions are more frequent
- rate of successful collisions increases
- greater rate of reaction
In a solid the particles can only vibrate so only the particles at the surface can react so rate is slower
How can you investigate the effect of surface area on rate of reaction?
Reaction between calcium carbonate and dilute hydrochloric acid
1) add dilute hydrochloric acid to a conical flask and stopper it with cotton wiol
2) place the flask on a balance next to a lump of calcium carbonate
3) tare the balance and remove the cotton wool, then drop the calcium carbonate lump into the acid and start a stop clock and put the cotton wool back
4) record the mass at regular intervals as the reading will decrease with CO2 escaping
5) use different forms of calcium carbonate (powder, small chips, large chips)
Why are catalysts useful?
Isn’t used up
- only small amounts can be used for a large reaction
- often contain expensive metals
How do catalysts work?
Provide an alternate reaction pathway with a lower activation energy
Greater proportion of particles have the required activation energy
How can you investigate the effect of a catalyst on the rate of a reaction?
Powdered manganese oxide catalyzes the decomposition of hydrogen peroxide
1) place hydrogen peroxide solution in a conical flask connected to a gas syringe
2) put varying masses of manganese oxide into the flask, stopper it and start the stop clock
3) record the time and volume of oxygen produced at regular time intervals
4) draw a graph to analyse the results
