C8-Rate Of Reaction Flashcards
What is the collision theory
The collision theory is a theory that states that particles must collide with sufficient energy in order to react .
What does the rate of reaction rely on
The rate of reaction relies on how frequently particles collide and with how much energy those particles collide with. Particles have to have enough energy in order to be able to react when they collide
What is the equation for rate of reaction
Rate of reaction = amount of reactants used up/ amount of products formed divided by time
What are the factors effecting rate of reaction
- Temperature
- concentration/pressure of gas
- surface area
- presence of catalysts
How does temperature affect rate of reaction
If the temperature of an object increases then the particles in that object start to move faster.
- As the particles move faster they collide more frequently
- There are also more collisions with sufficient energy due to the substance being heated which means that the rate of reaction increases
How does concentration/pressure affect rate of reaction
- If concentration increases there are more particles in the same volume of water
- If pressure increases the there are more particles per cm3
- This increases the frequency of collisions between particles as the particles are closer together. This means the rate if reaction increases
How does surface area affect rate of reaction
- If a solid object is broken apart then the surface area to volume ratio of that object increases
- This means that the volume of the object stays the same but the surface area that the particles have to collide with increases, this increases frequency of collisions and therefore increases rate of reaction.
How do catalysts affect the rate of reaction
Catalysts affect the rate of reaction by decreasing the activation energy needed for particles to collide. They provide an alternative reaction pathway with a lower activation energy. This means that particles can have less energy to react and collide successfully.
-Catalysts themselves do not get used up in the reaction
What are the pros and cons of catalysts
Pros
-They do not get used up in reactions
-They save money as less energy has to be used to start the reaction
Cons
-They can become poisoned when used in chemical plants
How can you measure the speed of a reaction
You can measure the speed of a reaction for a reaction that gives off gas by placing the conical flask with your reaction on a scales. As the gas is released the mass dissapears, you can measure the speed of a reaction by measure how quickly tthe mass drops
You can also measure the speed of the reaction by measuring the amount of gas given off using a gas syringe in a time interval.The more gas that is given off during the time interval the faster the reaction
How do you conduct the disappearing cross reaction
- Measure 50cm3 of sodium thiosulfate into a measuring cylinder
- Measure 10cm3 of hydrochloric acid in another cylinder
- mix the two solutions together in a beaker with a cross underneath it and time how long it takes for the cross to disappear
- Reapeat the experiment but vary the concentration of sodium thiosulfate by adding a volume of distilled water each time. Remeber to keep the volume of the solution the same
What is the equation for Energy released when bonds form
Energy released when bonds form = energy needed to break bonds- energy change of reaction
What is the problem with the dissappearing cross reaction
The problem is that each person has differnt eyesight strength so will be able to see the cross for different lengths of time
However if you use the same size printed cross the test should be fair
How can you conduct a rate of reaction practical with a measuring cylinder
- Use a measuring cylinder to measure 50cm3 of hydrochloric acid and place this in a conical flask
- attach the conical flask to a bung and delivery tube
- Now place the delivery tube in a container filled with water
- Place an upturned measuring cylinder also filled with water over the delivery tube
- Add a 3cm strip of magnesium to the hydrochloric acid and start a stopwatch - The reaction produces hydrogen gas which is trapped in the measuring cylinder
- Every ten seconds measure the volume of hydrogen gas in the measuring cylinder
- Continue until no more hydrogen is given off
- Repeat the experiment with a different concentration of hydrochloric acid . More hydrogen gas should be given off in less time if the concentration is higher
What happens if we heat hydrated copper sulfate
If we heat hydrated copper sulfate which is blue it reacts to form anhydrous copper sulfate which is white and water
The forward reaction is endothermic as energy is taken in
