Rates Of Reaction Flashcards
How to work out the rate of a chemical reaction
You can find out how quickly:
- the reactants are used up as they make products
- the products of the the reaction are made
Measuring the increasing volume of gas given off experiment
You can use the gas of a reaction to find out the rate of reaction. You do this by collecting the gas and measuring the volume given off at time intervals
Measuring the decreasing light passing through a solution experiment
Some reactions in a solution make a suspension of an insoluble solid (precipitate). This makes a solution go cloudy. You can use this the measure the rate at which the precipitate appears.
Draw a cross on paper and place the beaker of solution on top. Start stop watch when adding reactant and stop stopwatch when the cross disappears.
Measuring the decreasing mass of a reaction mixture experiment
You can measure it if the reaction gives off a gas. You can measure and record the mass at regulate time intervals
Mass won’t be lost if conical flask has a bung on it.
Formula for mean rate of reaction
Quantity of reaction or product / time
How to calculate R of R from a graph
Draw graph at specific time then calculate gradient
What is the minimum amount of energy that particles must have before they react?
The activation energy
Reactions are more likely to happen between particles if you:
• increase the frequency of the reacting particles colliding with eachother
• increase the energy they have when they collide
If you increase the chance of particles reacting, you also increase the R of R
What is collision theory
Reactions can only take place when particles of reactants come together. Reacting particles need to collide with enough energy to cause a reaction to take place.
What are four main factors which affect the R of R
- temperature
- surface area of solids
- concentration of solids or pressure of gases
- the presence of a catalyst
Surface area and reaction rate
The size of solid affects the R of R
The particles inside a large lump of solid are not in contact with the reactant particles in the solution, so they cannot react. The particles inside will have to wait for the particles on the outside to react first. * So the reaction is slower *
You can compare solids by looking at their SA:V ratio. The smaller the size of the pieces of material the larger it’s SA:V
The effect of temperature
Raising temp increases the rate of reaction, because:
- particles collide more often
- particles collide with more energy
When you heat up a substance, energy is transferred to its particles. Particles move around faster, so will collide more often increasing the R of R.
More energy - higher proportion of collisions exceeding the activation energy will result in the reaction taking place
Effect of concentration and pressure
Increases R of R because there are more particles of the reactants moving around in the same volume of solution. More chance they will collide.
Increasing pressure has same effect.
Effect of catalysts
Not used up so reduces energy costs and helps environment as operating at lower temps conserves non renewable resources and stops co2 entering our atmosphere.
Speeds up reactions by providing a alternative reaction pathway to the products, with a lower activation energy. Frequency of effective collisions goes up.
