C6 The Rate and Extent of Chemical Change random revision pages 142 - 148 Flashcards
What is rate of reaction a measure of?
How quickly reactants are changed into products
How can you tell what line on a rate graph respresnts the fastest rate of reaction? how can you tell?
It is the line that starts more steeply and goes flatter sooner than any of the others
What does collision theorty state must happen in order for a reaction to take place?
Particles must colide with enough energy to react (this is the activation energy).
What could you do in order to increase the speed at which particles in a reaction are moving?
increase the temperature
Explain why breaking up a solid into smaller pieces will increase its rate of reaction?
Breaking a solid into smaller pieces increases its surface area/surface area to volume ratio. More of the solid’s particles are available to particles of the other reactant and so collisions will be more frequent.
Catalysts provide an alternative reaction pathway. How does this pathway affect the rate of reaction? Explain your answer.
It increases the rate of reaction. The alternative pathway has a lower activation energy, so less energy is needed for the reaction to take place.
Which units are usually used to measure the volume of gas produced by a reaction?
cm³
What is meant by the ‘turbidty’ of a solution?
its cloudiness.
State one disadvantage of using a change in colour/turbidity to measure the rate of a reaction?
Any one from:
The results are very subjective.
You can’t plot a rate of reaction graph from the results.
A reaction produces a gas. State one thing you could measure to determine the rate of this reaction, and the piece of equipment you would use to measure it?
Any one from:
Measure the change in mass using a mass balance.
Measure the volume of gas given off using a gas syringe.
A student carries out an experiment to determine the effect of concentration on reaction rate. Why is it important that the student conrols all other variables in this experiment?
To make it a fair test./ So the student knows that any differences in reaction rate are due to differences in concentration and not a result of something else.
Give two things that should be kept constant when investigating the effect of acid concentration on the rate of the reaction between dilute acid and marble chips?
Any two from:
Mass of marble chips.
Surface area of marble chips.
Volume of acid.
Temperature
A student measures the rate of reaction between hydrochloric acid and magnesium using a mass balance. Why should the student plug the reaction vessel with cotton wool in this experiment?
To stop the acid spitting out (while still letting the gas escape).
Sodium thiosulfate and hydrochloric acid react to product a cloudy precipitate. Describe a method you could use to investigate the rate of this reaction?
E.g.
Add a set volume of dilute sodium thiosulfate solution to a conical flask.
Place the flask on a piece of paper with a black cross drawn on it.
Add a set volume of dilute hydrochloric aicd to the flask and start a stopwatch.
Measure the time taken for the cross to disappear from view.
Which variable should go on the x-axis of a rate graph? What about the y-axis?
x-axis = time
y-axid = amount of reactant used or amount of product formed.
What does a flat line on a rate of reaction graph tell you?
The reaction has finished.
What does this symbol tell you about a reaction?
> > > > > > > > > > > > > > «««««««<
The reaction is reversible.
True of false? Equilibrium can only be reached if the reaction takes place in a closed system. Explain your answer
True, because in order for equilibrium to be reached, none of the reactants or products can escape and nothing else can get in.
In the reaction shown below, more ammonium chloride breaks down and more the reaction mixture is heated. How could you change the conditions to increase the amount of ammonium chloride present?
ammonium chloride »_space;»
««_space; ammonia +
hydrogen chloride
Decrease the temperature.
If a reversible reaction gives out a certain amount of heat in one direction, what can you say about the energy change in the other direction?
The same amount of energy will be taken in./It will be endothermic
What principle is used to predict the effects of changing the conditions of a reaction at equilibrium?
Le Chatelier’s Principle
What will happen to the position of equilibrium in a reversible reaction if the temperature is increased, and the forward reaction is exothermic?
The equilibrium will move to the left/to favour the endothermic direction.
Explain how increasing the pressure would effect an equilibrium involving gasses?
The equilibrium position would shift towards the side of the reaction equation with fewer molecules of gas in order to reduce the pressure.
