rates and equilibrium (required practical) Flashcards
what is the rate of reaction?
how fast the reactants are changed into products.
what is an example of a slow medium and fast rate reaction?
slow - chemical weathering.
medium - magnesium and acid.
fast - burning.
how can you find the speed of a reaction?
the amount of product formed over time.
the amount of reactant used up over time.
what does a steep line mean on a rate of reaction graph?
the reaction is quicker.
what is collision theory?
chemical reactions occur when reactant particles collide with enough energy to react.
what does the rate of reaction depend on? (4)
- temperature.
- the concentration of a solution. or pressure of gas
- surface area. of the reactant
- the presence of a catalyst.
how does increasing the temperature increase the rate of reaction?
- when the temperature is increases the particles move faster.
- faster particles collide more frequently.
- the faster they move the more energy they have so more of the collisions have enough energy to make the reaction happen. activation energy
how does increasing the concentration or pressure increase the rate of reaction?
- a more concentrated solution means more particles are in the same volume.
- a higher pressure gas means the same number of particles occupy a smaller space.
- this makes collisions between reactant particles more frequent.
how does increasing the surface area increase the rate of reaction?
- if a reactant is a solid breaking it up increases its surface area to volume ratio.
- for the same volume of solid there is more area for collisions.
how does using a catalyst increase the rate of reaction?
- a catalyst speeds up a reaction without being used in the reaction.
- catalysts work to decrease the activation energy needed for a reaction to occur.
what is the formula for rate of reaction?
rate of reaction = reactant used / product formed ÷ time
how do you measure the rate of reaction using precipitation and colour change?
- if the initial solution is transparent and the product is a precipitate that clouds the solution.
- observer a mark through the solution and time how long it takes to disappear.
- if the reactants are coloured and the products are colourless you can time how long it takes to lose or gain colour.
how do you measure the rate of reaction using change in mass?
if a gas is released the mass disappearing can be measured on a scale.
how do you measure the rate of reaction using the volume of gas given off?
use a gas syringe to measure the volume of gas given off.
how do you investigate the effect of concentration on the rate of reaction? (required practical)
- add a set volume of dilute hydrochloric acid to a conical flask and place it on a mass balance.
- add some magnesium ribbon to the acid and plug the flask with cotton wool.
- start a stopwatch and record the mass on the balance and take more readings at regular intervals.
- plot the results on a table and work out the mass lost at each reading and plot a graph.
- repeat the experiment with more concentrated acid solutions.
how do you find the reaction rate at a particular point on a graph?
use a tangent. don’t make the mistake again
how do reversible reactions reach equilibrium?
- as reactants react their concentration falls and so the forward reaction will slow down.
- as more products are made their concentration increases so the backward reaction will speed up.
- at equilibrium both reactions are still happening but there’s no overall effect as the concentrations of reactants and products have reached a balance.
equilibrium is only reached if the reaction takes place in a closed system as no substances can escape
what are the concentrations like if the equilibrium lies to the right?
the concentration of products is greater than the reactants.
what are the concentrations like of the equilibrium lies to the left?
the concentration of reactants is greater than the products.
if a forward reaction is exothermic what is the backwards reaction?
endothermic. energy releases is equal to energy taken in
what is le chatelier’s principle?
if you change the conditions of a reversible reaction at equilibrium the system will try to counteract these changes.
how does temperature effect the equilibrium position?
- all reactions are exothermic in one direction and endothermic in the other.
- if you decrease the temperature the equilibrium will move in the exothermic direction to produce more heat. the system wants to counteract the temperature change
- if you raise the temperature the equilibrium will move in the endothermic to try and decrease the temperature.
how does pressure effect the equilibrium position?
- changing the pressure only affects equilibrium involving gasses.
- if you increase the pressure the equilibrium move in the direction where there are fewer gas molecules. to try and reduce the pressure
- if you decrease the pressure the equilibrium moves in the direction where there are more gas molecules. to try and increase the pressure
- use a balanced symbol equation to work out which side has more molecules of gas.
how does concentration effect the equilibrium position?
- if you change the concentration of either the reactants or products the system is no longer at equilibrium.
- the system will try to bring itself back to equilibrium.
- if you increase the concentration of the reactants the system will make more products.
- if you decrease the concentration of the products the system will reduce the amount of reactants.
