Rates of Reaction Flashcards
Hoe would you measure the rate of the reaction of CaCO3 with HCl?
Place marble chips in a conical flask and put cotton wool on top. Place this on a weighing scale and zero it. Pour in dilute hydrochloric acid and measure the mass every minute thereafter.
Why is cotton wool used in this experiment?
measuring the rate of reaction of CaCO3 with HCl
To allow the carbon dioxide to escape but to stop any acid spraying out.
What results will you expect for this experiment?
measuring the rate of reaction of CaCO3 with HCl
The reaction is fastest at the beginning and then slows down until all the hydrochloric acid has been used up. There will still be unreacted marble chips in the conical flask.
Explain collision theory
Reactions can only happen when particles collide. As the acid particles get used up the collision rate decreases and the reaction slows down.
What is the relationship between rate of reaction and surface areas? Why?
The higher the surface area the faster the reaction. There is a larger area available for the particles to react with.
What is the relationship between rate of reaction and concentration of the acid? Why?
The higher the concentration the faster the reaction. Increasing the concentration increases the number of times the particles hit per second.
What is the relationship between rate of reaction and temperature? Why?
The higher the temperature the faster the reaction. The particles have more energy and move faster so hit each other more often.
Roughly how many degrees would you need to increase the temperature by to double the rate of reaction?
10 degrees.
What is the relationship between rate of reaction and pressure? Why?
If reactants are gases the higher the pressure the faster the reaction. If you have a fixed amount of gas the pressure is increased by decreasing the volume the particles are in. This means they are closer together and hit more frequently.
What is a catalyst?
A substance that speeds up chemical reactions without getting used up in the process.
What is commonly used as a catalyst of the decomposition of hydrogen peroxide?
manganese dioxide
MnO2
Describe an experiment to measure how rates of reaction are effected by catalysts:
Put hydrogen peroxide in a conical flask with a small weighing bottle containing manganese oxide.
Attach a delivery tube to the flask and place this in a beaker of water with a small measuring cylinder filled with water above the delivery tube.
Measure how long it takes for 5cm3 of gas to be released.
Shake the flask continuously to knock the bottle and so that the manganese oxide mixes with the hydrogen peroxide.
Set up the experiment again and change the conditions of the catalyst.
How can you prove that the manganese oxide was a catalyst and not a reactant?
Weigh it before you add it and then reweigh it at the end. You may have to separate it from the liquid using a weighed filter paper. Wait for the filter paper and residue to dry and then reweigh it. If it is the same then it has not been used up and it is a catalyst.
What does it mean if a reaction is slow in terms of activation energy?
It means that very few of the collisions occurring have the activation energy required for the reaction to happen. When most of the collisions occur the particles will just bounce off of each other.
How does a catalyst work?
Adding a catalyst provides an alternate route with a lower activation energy (do not just say lowers activation energy, the original route is still there). If the activation energy many more collisions are likely to be successful. The reaction happens faster because the alternative route is easier.
