C6 - The Rate and Extent of Chemical Change Flashcards
What is rate of reaction?
The change in amount of a reactant or product per unit time.
What 2 factors does rate depend on?
Frequency of collisions.
Energy of collisions
What happens when you increase the temperature of a reaction?
Particles have more kinetic energy, so there are more frequent collisions but also more energetic collisions.
What happens to the rate of reaction as the reactant runs out?
As the reactant runs out, the concentration decreases, so the collision frequency is slower, meaning rate of reaction is slower.
What is a dynamic equilibrium?
When the rate of the forward and backward reactions are the same, so the net concentration remains constant.
What is Le Chatelier’s principle?
If a change is made to the equilibrium, the equilibrium will act to oppose the change.
If there are more reactants where does the equilibrium lie?
Left
If there are more products where does the equilibrium lie?
Right
If the forward reaction is endothermic and the backward reaction is exothermic, and there is an increase in temp. where does the equilibrium lie?
Right - to decrease temp.
If the forward reaction is endothermic and the backward reaction is exothermic, and there is an decrease in temp. where does the equilibrium lie?
Left - to increase temp.
If there are 4 mol of reactants and 2 mol of products, and there is an increase of pressure where will the equilibrium lie?
Right - to decrease pressure
If conc. of reactants is increased, what is the effect on equilibrium?
Right
If conc. of products is decreased, what is the effect on equilibrium?
Right
How is rate of reaction calculated?
rate of reaction = amount of reactant used or product formed / time
State 5 factors affecting the rate of a reaction.
Catalysts
Temperature
Conc. of reactants
Pressure of gases
Surface area
What is collision theory?
Chemical reactions can only occur when reacting particles collide with each other with sufficient energy.
What is a reversible reaction?
When the products of a reaction can react backwards to produce original reactants.
What is activation energy?
The minimum amount of energy particles must collide with for a reaction to happen.
What is a catalyst?
A substance that can increase the rate of a reaction while remaining unchanged by the end of the reaction.
What do catalysts do to the activation energy of the reaction?
They lower the activation energy by providing an alternative route meaning there is a higher chance that more particles will react.
Why are catalysts economical?
They require lower temperatures to start the reaction.
How is rate of reaction calculated?
amount of reactant used or product formed / time
What are the various units for reaction time?
g/s (mass/time), cm3/s (volume/time), mol/s (moles/time)
Name 3 ways of measuring rate of reaction.
Loss in mass of reactants.
Volume of gas produced.
Time for a solution to become opaque.
Describe measuring the rate by monitoring mass loss.
Place reaction flask on a balance. In reaction of metal carbonate + acid a gas is given off.
Record decrease of mass in time intervals.
Describe measuring the rate by monitoring volume of a gas.
Connect a gas syringe to a reaction flask and measure the volume of a gas formed in time intervals.
Describe measuring the rate by monitoring disappearance of a cross.
Put a reaction flask on a piece of paper with a cross on it. Mix the reactants, and measure how long it takes for a cloudy mixture to conceal the cross.
5 factors that affect the rate of a reaction.
Concentration of reactants.
Pressure of gases.
Surface area.
Temperature.
Catalysts.
What must happen for a reaction to occur?
Particles must collide with at least a minimum amount of energy.
How to find rate of reaction from a graph at a certain time?
gradient of tangent
How does concentration link to rate of reaction?
Con. increases = faster reaction
More reactants = more frequent collisions
How does pressure link to rate of reaction?
Increases number of gas molecules in a given volume.
So, frequency increases so increases rate of reaction.
How does surface area link to rate of reaction?
Increase in surface area increases frequency of collisions and so increases rate of reaction.
What is an enzyme?
A molecule that acts as a catalyst in a biological system.
Describe effect of a catalyst on the position of an equilibium.
No effect.
Forward and backward reactions sped up equally.
However, means equilibrium is achieved quicker.
What happens as the reactant runs out in a non-reversible reaction?
Conc. decreases so collision frequency is slower, rate of reaction is slower.
How can you increase the surface area of a solid?
Break it down into smaller pieces.
