Combined Chemistry - C6 The rate and extent of chemical change Flashcards
What two equations can be used to measure the rate of a reaction?
mean rate of reaction = (quantity of reactant used) / time
mean rate of reaction = (quantity of product formed) / time
Calculate the mean rate of reaction for the following examples (give the correct unit):
a) A reaction producing 50 cm3 of gas in 5 s.
b) A reaction where 5 g of calcium carbonate completely reacts in 10 s.
*These are just examples, you should be able to calculate rate of reactions for any given reactions.
a) 10 cm3/s
b) 0.5 g/s
Higher Q. Calculate the rate of reaction when 2 moles of magnesium oxide reacts in 4 seconds.
*This is just an example, you should be able to calculate rate of reactions for any given reactions.
0.5 mol/s
Which reaction shows the fastest rate of reaction? A, B or C?
A
What is the name for the straight line drawn next to the curve at the point indicated by the arrow?
Tangent
Higher Q. How would you calculate the rate of the reaction at the point indicated by the arrow?
- Draw a tangent at that point
- Calculate the gradient of the tangent
List the 5 things that can affect the rate of a reaction.
- Concentration (of solutions)
- Pressure (of gases)
- Surface area (of solids)
- Temperature
- Catalysts
What is the name for the minimum amount of energy needed for a reaction to happen?
Activation Energy
What theory states that chemical reactions only occur when reacting particles collude with enough energy?
Collision Theory
Explain how temperature affects the rate of reaction.
- Increasing temperature…
- …Increases the frequency of collisions…
- …The collisions are more energetic.
Explain how surface area affects the rate of reaction.
- Increasing the surface area …
- …increases the frequency of collisions…
- …and so increases the rate of reaction.
Explain how concentration affects the rate of reaction.
- Increasing the concentration…
- …increases the frequency of collisions…
- …and so increases the rate of reaction.
Explain how pressure affects the rate of reaction.
- Increasing the pressure…
- …increases the frequency of collisions…
- …and so increases the rate of reaction.
How does a catalyst work?
- Catalysts increase the rate of reaction…
- …by providing an alternative pathway for the reaction…
- …with a lower activation energy.
What is a catalyst?
Something that increases the rate of a reaction without being used up in the reaction.
How would you add a line to show the effect of a catalyst on the reaction profile below?
What is the symbol for a reversible reaction?
If a reversible reaction is endothermic in forward direction, what will it be in the reverse direction?
Exothermic
What does ‘equilibrium’ mean?
In a reversible reaction, the forward and reverse reactions occur at exactly the same rate.
Higher Q. What is Le Chatelier’s Principle?
The idea that if you change the conditions(such as temperature and pressure) of a reversible reaction at equilibrium, the system will try to counteract the change.
Higher Q. What effect will increasing the concentration of a reactant have on a reversible reaction?
- More products will be formed
- Until equilibrium is reached again
Higher Q. For a gaseous reaction at equilibrium, what would be the effect of…
a) … increasing pressure
b) … decreasing pressure
a) Equilibrium position will shift towards the side with the smaller number of molecules
b) Equilibrium position will shift towards the side with the larger number of molecules
Higher Q. For a reversible reaction at equilibrium, what effect will increasing temperature have on…
a) … the endothermic reaction
b) … the exothermic reaction
a) Endothermic reaction: The amount of product increases
b) Exothermic reaction: The amount of product decreases
Higher Q. For a reversible reaction at equilibrium, what effect will decreasing temperature have on…
a) … the endothermic reaction
b) … the exothermic reaction
a) Endothermic reaction: The amount of product decreases
b) Exothermic reaction: The amount of product increases
