Rates of chemical change (P2) Flashcards
(14 cards)
What is collision theory?
Chemical reactions can only take place when the reacting particles collide with each other. The collisions must have sufficient energy.
What is the rate of reaction determined by (in terms of particles)?
The frequency of successful collisions.
How does concentration affect rate of reaction in a solvent and in a gas?
Solvent: increased concentration means more particles in the same volume of solvent so collisions of particles are more frequent.
Gas: increased concentration means the same number particles in a smaller space so more frequent collisions.
How does temperature affect the rate of reaction?
.Increased temperature means the particles travel faster which means more frequent collisions
.Increased temperature means the particles will have more energy so more of the collisions will have enough energy to make the reaction start
How can you increase the surface area to volume ratio of a solid? How does this affect the rate of reaction?
To increase the surface area to volume ratio, you can break the solid into smaller pieces.
This means that for the same volume of the solid, the particles around it will have more area to work on so the collisions will be more frequent.
How do catalysts affect the rate of reaction?
By lowering the activation energy needed for the reaction to occur.
What is the equation for rate of reaction?
Amount of reactant used up or amount of product formed/ time
Explain the disappearing cross practical
Sodium thiosulfate and HCL are colourless, clear solutions. They react to form yellow precipitate of sulfur
1) Add a certain volume of dilute sodium thiosulfate to a conical flask
2) Place the conical flask on a white piece of paper with a black cross on it
3) Add a certain volume of dilute HCL to the flask and start the stopwatch
4) Look down at conical flask and stop stopwatch when you can no longer see the black cross
5) Repeat with different concentrations of HCL
6) Repeat steps 1-5 to calculate a mean for each concentration
What’s the problem with the disappearing cross practical?
It’s not reproducible as different people have different eyesight.
How can you measure how much gas was given off in a reaction?
.Change in mass
.Using a gas syringe
Explain the rate of reaction experiment that measure gas given off.
HCL and magnesium react to produce hydrogen gas
1) Use a measuring cylinder to add a 50cm^3 of HCL into a conical flask
2) Attach the conical flask to a bung and a delivery tube
3) Place the delivery tube into a container filled with water
4) Place an upturned measuring cylinder (filled with water) over delivery tube
5) Add a 3cm strip of magnesium to conical flask and start stopwatch
6) Measure the volume of hydrogen gas in the measuring cylinder at regular intervals until no more hydrogen is given off
7) Repeat the experiment with different concentrations of HCL
If in one direction, a reaction is exothermic, what can you say about the opposite direction.
It is endothermic
True or false: different amounts of energy is transferred when you go in different directions of a reversible reaction
False- always the same amount of energy transferred.
When a reversible reaction occurs in sealed apparatus, when is equilibrium reached?
When the forwards and reverse reaction occur at the same rate.
