Rates Of Reaction Freesciencelessons Flashcards
What is collision theory?
Chemical reactions can only take place when the reacting particles have sufficient energy and collide with each other
What is rate determined by?
The frequency of successful collisions
What do catalysts do in chemical reactions?
They increase the rate of the chemical reaction but are not used up during the reaction which allows us to carry out reactions quickly without needing to increase the temperature which saves money
How do catalysts work?
They increase the rate by providing a different pathway for the reaction which lowers activation energy so particles now require less energy to reach the activation energy barrier so more particles can successfully collide
Why are catalysts not included in chemical equations?
Because they are not used up
Example of a catalyst
Enzymes in a living organism
Define reversible reactions
Products can react to reform the original reactants
How can we change the direction of the reaction?
By changing the conditions e.g. forwards by heating and backwards by freezing
What does heating mean in reversible reactions?
Energy goes in so its endothermic therefore the reversible reaction acts in the opposite direction which is exothermic but THE SAME AMOUNT OF ENERGY IS TRANSFERRED
What is an example of a reversible reaction?
Hydrated copper sulfate ⇌ anhydrous copper sulfate (white) + water
What is equilibrium?
When the forward and reverse reaction take place at the same rate
What is the rule of equilibria?
If a system is at equilibrium and a change is made to the conditions, the system reacts to counteract the change
Why does concentration change?
Concentration of all substances change until equilibrium is reached
Example of concentration change
2NO2 ⇌ N2O4
(increase in NO2 concentration so more NO2 formed)
What happens to temperature when reverse reaction takes place?
Energy is taken in so temperature decreases
Explain what happens when we increase temperature in a system
If we increase the temperature of this specific system the equilibrium shifts to the left to reduce the temperature because the reverse reaction is endothermic taking energy in so temperature falls
What does effects of pressure mean?
Pressure effects reactions involving gases so the pressure of the gas depends on the number of molecules
What happens when you increase the pressure in a reversible reaction?
If we increase the pressure at equilibrium it shifts to the side with a smaller number of molecules
What happens when you decrease the pressure in a reversible reaction?
If we reduce the pressure the position of equilibrium shifts to the side with a larger number of molecules
What effect does changing pressure have if there is equal amount of molecules on each side?
Changing pressure has no effect on the position of equilibrium
What is the equation for mean rate of reaction?
Quantity formed / time taken
Why does the slope get less steep in reactions?
Most reactant molecules have already reacted turning into product
What is quantity measured in?
Grams
What is gas amount measured in?
Cm3
How do you use a tangent to determine rate?
Draw on a tangent on the slope and create a triangle using the graph to find the lengths of the sides and do Y/X
Why are reactions rapid at the start?
Because there is a large number of reactant molecules so a large number of collisions each second
What is the link between concentration and rate?
They are directly proportional so if concentration goes up so does rate making a faster reaction and more products
How do we know if a measurement is reproducible?
It can be repeated by another person using a different technique and still get the same result
What is the issue with the rates of reaction practical?
Different people have different eyesights so some can see the cross for longer so they may get different results
Summarise the rates of reaction practical.
Add 10cm3 sodium thiosulfate to a measuring cyclinder and then into a conical flask,place the conical flask on a printed cross, add 10cm3 of hydrochloric acid,swirl the solution and start the stopwatch until the solution gets cloudy,stop the stopwatch when you can no longer see the cross, repeat the experiment with a lower concentration of sodium thiosulfate and calculate a mean
What do both types of the rates of reaction practical show?
The greater the concentration, the faster the reaction therefore the finding is reproducible as its found from two different experiments
What do particles in a solution react with?
Only the particles on the surface of a solid
What does an increase of surface area mean for the rate?
More collisions as surface area increases so rate increases
Why does greater surface area mean faster rate?
Smaller blocks of a solid have a greater surface area to volume ratio so there are more particles on the surface so more collisions per second,increasing the rate of reaction
How can we measure volume of gas?
With a gas syringe
What does the measurement of CO2 gas show?
CO2 is lost, more produced so mass decreases
What does exothermic mean for products and reactants?
Product has less energy than reactants
What does distance from reactant to peak show?
Activation energy (minimum amount of energy particles must have for a reaction to occur)
What does the sizes of arrows show?
Energy of each particle
What happens with two particles of sufficient energy?
Two particles with a large amount of energy can collide successfully as they have enough energy to overcome the activation energy barrier
What does increase in temperature mean for rate?
Increase of temperature = increase of rate of chemical reaction as it increases the energy of particles so they move faster increasing frequency of collisions
