Year 8 Chemical Formulae And Equations And Rates Of Reaction Flashcards
What factors affect the rate of reaction?
Concentration of reactants Pressure (only for gases) Particle size (SA) Light Temperature Catalyst
How does the concentration of the reactants affect the rate of reaction?
The higher the concentration the faster the rate of reaction
How does particle size (SA) affect the rate of reaction?
The bigger the SA the faster the rate of reaction
How does the temperature affect the rate of reaction?
The higher the temperature the faster the rate of reaction
How does the catalyst affect the rate of reaction?
The larger the catalyst, the faster the rate of reaction
What is activation energy?
It represents the minimum energy needed for the reaction
Describe an experiment to measure the effects of increased concentration
Reaction of magnesium metal with dilute hydrochloric acid
It gives off hydrogen gas, which can be measured with a mass balance
Time is the independent variable
Mass loss is the dependent variable
Take reading’s of mass at regular time intervals and put them in a table and work out the loss in mass for each reading.
Repeat it with more concentrated acid solutions, but always keep the SAME amount of magnesium.
SAME VOLUME of acid, just different concentration
The higher the concentration, the steeper the gradient, and the reaction finishes a lot faster
Describe an experiment with a change in temperature
Sodium thiosulfate and hydrochloric acid produce a cloudy precipitate
Both solutions are clear
They react to form yellow precipitate of sulphur
Time how long it takes for a black mark to disappear
The reaction can be repeated for solutions at different temperatures
=Quite hard to do –> unsafe to directly heat acid
Use a water bath to heat both solutions to the right temp before mixing them
Same amount of liquid each time
The higher the temp the faster the rate of reaction, therefore the less time it takes for the black mark to disappear
Temperature - independent variable
Time taken for mark to disappear - dependent variable
Describe an experiment with changing surface areas
Hydrochloric acid and marble chips
Measure volume of gas evolved with a gas syringe and take readings at regular intervals
Repeat with same volume of acid and mass of marble chips, but CRUSH them up slightly
Repeat with POWDERED marble chips
Larger the SA, the more collisions between the chips, so rate of reaction is faster.
(Powdered has the biggest SA)
Has the fastest reaction and MORE GAS is evolved overall
What is the collision theory?
The rate of reaction simply depends on how often and how hard the reacting particles collide with each other. Particles have to collide in order to react, and they have to collide hard enough (with enough energy).
More collisions…
Increase the rate of reaction
Collision theory in terms of higher temperature
When the temp is increased the particles have more energy and therefore move quicker. If they’re moving quicker, they’re going to collide more frequently
Collision theory in terms of concentration (or pressure)
If a solution is made more concentrated, it means that there are more particles of a reactant around between the water molecules, which makes collisions between the important particles more likely.
In a gas, increasing the pressure means that the particles are more squashed up together so they are going to collide more frequently.
As a reaction progresses, there are fewer and fewer reactant particles, so they collide less frequently and the rate of reaction slows down
Collision theory in terms of surface area
If one of the reactants is a solid, then breaking it up into smaller pieces will increase its SA. This means that the particles around it in a solution will have more area to work on, so there will be more useful collisions more often.
Collision theory in terms of catalysts
A solid catalyst works by giving the reacting particles a surface to stick to. They increase the number of SUCCESSFUL collisions by LOWERING the activation energy.
