Unit 6 - Rate/Extent of Chemical Reactions Flashcards
How do we measure rate of reaction?
Change in quantity ÷ time
What is an experiment we can do to test rate of reaction?
Hydrochloric acid + sodium thiosulphate in conical flask to make cloudy solution (higher turbidity.) Place cross beneath flask and measure time taken for cross to disappear (at different concentrations of acid)
How do you know where the end point of a reaction is from a graph (when the reaction has stopped?)
When the graph levels out and the gradient = 0
How do we calculate rate of reaction at any point from a graph?
Draw a tangent and find gradient
How can we increase the rate of reaction?
-Increasing surface area (Particles collide more frequently)
-Increasing concentration (Particles collide more frequently)
-Increasing pressure (Particles collide more frequently)
-Increasing temperature (Particles collide more frequently, particles collide with more energy so more likely to have successful collisions)
-Catalyst (Provides alternate pathway requiring less energy)
What is a reversible reaction and what is an example?
Reactions that can be turned from reactants to products or from products to reactants. An example is the Haber process where ammonia is produced. (N2+3H2 ⇌ 2NH3)
What does it mean when a reversible reaction is in equilibrium?
The overall quantity of both sides remain the same as the rates of both reactions are the same.
What is Le Chatelier’s principle?
If a system at equilibrium is subjected to a change, the system will adjust to counteract the change.
What effect does temperature have on reactions at equilibrium?
Hotter temperatures - favours endothermic
Lower temperatures - favours exothermic
What effect does does pressure or concentration have on reactions at equilibrium?
Higher concentration or pressure causes the equilibrium to shift to the side with fewer moles so more will be made. For example, in the Haber process, the forward reaction (which makes ammonia) would be favoured as there are fewer moles so more ammonia is made
What happens in a reversible reaction in a closed system (no particles or energy going in or out?)
Both reactions continually take place
What are the conditions for the Haber process?
450 degrees celsius and 200 atmospheres
Why are these conditions a compromise?
The high pressure favours the forward reaction while higher temperature increases the rate of reaction but negatively favours the reverse reaction (not good)
Why do we compromise the conditions for the Haber process?
To maximise ammonia yield while ensuring the reaction happens at a reasonable rate
