C8: Rates and Equilibrium Flashcards
What is the rate of reaction?
How quickly reactants turn into products. Can be found using tangent on a graph.
What is the equation for rate of reaction?
Rate of Reaction (g/s, cm3/s, mol/s) = Amount of Reactant Used / Time
Or
Rate of Reaction = Amount of Product Formed / Time
How does a reaction take place?
When the particles of the reactants have enough successful collisions with enough energy.
Reactions are more likely to happen if you increase the frequency of reacting particles colliding with each other and by increasing the energy they have been colliding.
Why does a greater surface area increase the rate of reaction?
A greater surface area to volume ratio means that more particles are exposed to react so it increases the frequency of collisions between reacting particles.
How does temperature affect the rate of reaction?
By increasing the temperature, more energy is transferred to the reacting particles meaning they move around faster. This causes the particles to collide more frequently with more energy
An increased proportion of particles exceeding the activation energy increases the rate that particles collide.
How does concentration affect rate of reaction?
Increasing the concentration of the reactants in a solution means there are more reacting particles. This means particles are more crowded together, increasing the frequency of collisions. Increasing the pressure of gases has the same effect, as there are more gas particles in a given space.
How does a catalyst affect the rate of reaction?
They provide an alternate reaction pathway with a lower activation energy. This means a higher proportion of particles have enough energy to collide at a greater frequency and have more successful collisions.
Other than increasing the rate of reaction, why is a catalyst used?
It means less energy needs to be paid for so they speed up reactions and reduce energy costs.
Helps the environment as fossil fuels and non renewable resources don’t need to be used.
Describe method of how to investigate rate of reaction by measuring the volume of gas produced.
- Measure 50cm3 of hydrochloric acid using a measuring cylinder and pour it into a 100cm3 conical flask.
- Have a gas syringe set up with the conical flask.
- Add a 3cm strip of magnesium ribbon to the conical flask and start a stopwatch.
- Record the volume of gas given off every 10 seconds until no more gas is given off.
- Repeat using a different concentration of hydrochloric acid and plot results for each concentration, of volume produced against time.
Describe method to investigate rate of reaction using colour change.
- Measure 10cm3 of sodium thiosulfate solution into a conical flask.
- Dilute the solution by adding 40cm3 of water and put conical flask on black cross.
- Measure 10cm3 of hydrochloric acid and add to flask, stir gently and start stopwatch.
- Look down conical flask and stop the stopwatch when you can no longer see the black cross.
- Repeat using different volumes of sodium thiosulfate solution and water to change the concentration.
- Repeat investigation 3 times and calculate mean time for each concentration.
What are reversible reactions?
They are reactions when the products can react again to form the original reactants.
E.g. Hydrogen + Nitrogen = Ammonia
Are reactions in reversible reactions exothermic or endothermic?
One reaction is exothermic and the other is endothermic. The amount of energy transferred to the surroundings in one direction is equal to the amount of energy taken into the other.
How does a reversible reaction reach equilibrium?
In closed systems, a reversible reaction reaches equilibrium if the rate of the forward reaction is equal to the rate of the reverse reaction.
What is Le Chatelier’s Principle and why is it important?
It is that whenever a change in conditions is introduced to a system at equilibrium, the position of equilibrium shifts to cancel out the change.
Important in chemical industry as chemists can find out what conditions give as much product possible in a short time.
What happens if the concentration of products or reactants increases?
The position of equilibrium shifts towards side with lower concentration so that enoguh of either products/reactants is produced until equilbrium is reached again.
