Rates Of Reaction Flashcards
What is the rate of reaction?
The speed at which a reactant is used up or a product is made
What is the units for the rate of reaction?
g/S or cm^3/s
Equations to work out the rate of reaction
Rate of reaction = Amount of reactant used up / time
Rate of reaction = amount of product formed / time
What does the collision theory state?
That a chemical reaction can only occur when reacting particles collide with each other with sufficient energy.
What is activation energy?
The minimum amount of energy particles must have to react.
How do you get a successful collision to happen?
If particles collide with energy greater than the activation energy, a successful collision occurs. The more successful collisions per second, the faster rate of reaction.
As the reactants are used up what happens?
The particles collide less often and the reaction slows down.
How can we increase the rate of reaction?
Increasing the number of collision per second
Increasing the number of particles
Decreasing the activation energy
The effect of particle size on the rate of reaction experiment - what do you use?
Small and large marble chips made out of calcium carbonate. You react it with hydrochloric acid to produce carbon dioxide gas.
What is the cotton wool used for in the effect of particle size experiment
To stop any acid from spitting out and allow the carbon dioxide to escape
What is the independent and control and dependent and where do they go On a graph?
Independent Variable (the one that is changed - x axis) - Dependent Variable (the variable being measured - y axis) - Control Variable (kept the same) -
What is the independent, dependent and control variable in the marble chips experiment?
Independent - the size of chips
Dependent - decreasing mass
Control - weight of chips and concentration of hydrochloric acid.
Why might you find a negative mass after adding the content into a conical flask?
Because the carbon dioxide is escaping through the cotton wool
How do you work out the average rate of reaction?
Pick a certain time and go up till you get to the line and measure from there. For example, I pick 1min and it goes to 0.47. You do 0.47/1 = 0.47g/min
Conclusion for marble chips experiment
Large marble chips - small surface area and small marble chips - large surface area.
If the reactants are smaller, the rate of reaction increases.
Smaller particles of solid have a large surface area so they collide more often and there are more successful collisions per second therefore a faster rate of reaction.
What is the independent variable, dependent and control for the effect of concentration experiment
Independent - volume of water
Dependent- volume of gas produced
Control - surface area of Chips and mass of chips
What happens to the rate of reaction over time in the effect of concentration experiment?
The rate of reaction slows down and slowly stops. Because the reactants are being used up.
Should the volume of carbon dioxide be the same for all the concentrations and why?
Yes because we have the same number of acid particles and so the volume of carbon dioxide should be the same.
Which concentration would have the steepest gradient in the effect of concentration experiment?
15cm^3 of acid and 20cm^3 of water because it is the most concentrated and therefore a faster rate of reaction
How would you work out the initial rate for the effect of concentration experiment?
The volume of gas produced/ Time
For example at 30seconds the volume was 15 for 30cm^3 water then it would be 15/30
Using the collision theory explain why 20cm^3 water has the fastest rate of reaction?
Increasing concentration increases the number of particles per unit volume. There is a greater chance of the particles colliding so more successful collisions per second and therefore the rate of reaction increases.
What is the independent, dependent and control variable for the effect of temperatures experiment?
Independent - time taken for cross to disappear
Dependent - volume of sodium thiosulphate and hydrochloric acid
When the temperature increases, the rate of reaction increases why? Two methods to explain this
Collision frequency - the particles have more energy so move faster and collide more often
Activation Energy - more particles that have more energy greater than the activation energy equal a higher percentage of collisions that are successful per second.
If the pressure of a gas increases why does the rate of reaction increases?
As the pressure increases, there are more particles in a given volume so they collide more often and so there are more successful collisions per second.
What is a catalyst?
A substances that increases the rate of a reaction but is chemically unchanged at the end of reaction
What is the independent, dependent and control variable of the effect of catalysts experiment
Indepdent - with or without catalyst
Dependent - amount of gas reproches
Control variable - volume of water and hydrogen peroxide
If a catalyst is used what happens to the rate of reaction, explain using collision theory.
If a catalyst is used, the rate of reaction increases but the catalyst is unchanged (not used up).
Catalysts provide an alternative route for the reaction with a lower activation energy so more particles have energy greater than the activation energy and more successful collisions per second.
Catalysts reduce energy costs
Look at folder for…
Energy profile diagrams for endothermic and exothermic reactions
If two experiments contain the same number of particles, how would their graphs look
Graphs will finish at the same heigh as the same amount of products is produced in the end.
If two experiments contain half the number particles how will the graph look?
It will produce half amount of product so the graph will finish at half the height
Equations for the effect of particle size and effect of catalyst experiment
Effect of particle size - CaCO3 + 2HCl —> CaCl2+ CO2 + H2O
Catalyst - 2H2O2 —> 2H2O + O2
How do you prove that a catalyst is not used up?
Filter it off, wash and dry it - the mass should the be the same before and after
Name a catalyst and give a use
Finely divided iron - to produce ammonia
