C8 - Rates of Reaction Flashcards
(24 cards)
What is the rate of reaction?
The quanity of product formed over time.
How do you measure the rate of reaction?
- How fast a reactant is used up
- How fast the product is made
Formula for calculating the rate of reaction
Reactant used or product formed/time take (s)
Why is cotton wool placed in the mouth of the flask?
It allows gas out but prevents any materials from being ejected from the flask (if the reaction is vigurous)
Why is measuring the rate of reaction from loss in mass not suitable for hydrogen and other gases?
- They have a small relative mass
- Loss in mass may be too small to measure
What equipment is used to determine the rate of reaction?
- Gas syringe
- Conical Flask
- Reaction Mixture
How do you measure the rate of precipitation?
1) A piece of paper with a black cross on it is placed
2) Add an amount of sodium thiosulphate solution to a conical flask
3) Add the acid and start the timer
4) When looking from above, when the cross dissapears, you stop the timer
How does a precipitation reaction form a solid precipitate?
- 2 clear solutions are mixed together
- The precipitae clouds the reaction mixture, so if the piece of paper is placed under a flask with a cross on it, you can see the cross dissapear
What are 2 Disadvantages of the Rate of precipitation reaction?
- People may not agree on the exact moment that the cross dissapears
- Only one data point is produced per experiment, so you cant plot a rate reaction graph
What does a steeper gradient mean in correlation to the rate of reaction?
The steeper the gradient, the faster the rate of reaction
What happens to the reactant if the line is horizontal?
- The reactants are being used up so the line becomes less steep and eventually become horizontal, meaning the reaction has finished
How do you find the gradient of a graph
- Drawing a tangent at a curve
- Finding the difference in Y/X
What does the curved section of a graph tell us?
The relationship between rate and factor being measure are not directly proportional, so the rate is different at each point
What are the 5 factors that affect the rate of reaction?
- Pressure
- Concentration
- Temperature
- Surface area
- Use of a catalyst
What happens to the rate of reaction when the concentration is increased?
It also increases
How does a catalyst incrwase the rate of reaction?
- It reduces the activation energy
What does lowering the activation level do?
- more particles will have enough energy to react when they come together
What is collision theory?
when chemical reactions only occur when the reactant particles collid with sufficient energy to react
What is the activation energy?
The minimum amount of energy needed
What happens if a particle collides with insufficient energy?
They will have unsuccessful collisions and bounce off eachother
How would you increases the rate of reaction? (c)
number of successful collisions need to increase
How does increasing concentration increase the rate of reaction?
- More reactant particles in a volume so more successful collisions, increasing the rate of reaction
How does increasing temperature increase the rate of reaction?
- Particles have more kinetic energy that the required activation energy
- More frequent and successful collisions per second
How does increasing the surface area increase the rate of reaction?
- More surface area of the particles are now exposed to the other reactant, making more collisions per second
