Rates of Reaction (Paper 2) Flashcards
What is meant by rate of reaction
How quickly reactants turn into products
Phrase used to describe how quickly reactants turn into products
Rate of reaction
2 things to measure when calculating rate of reaction
How quickly the reactant is used up
How quickly the product is produced
True or false, some reactions can take years or decades
True (e.g rusting of iron)
True or false, some reactions take place in just a fraction of a second
True e.g fireworks
Equation to measure how fast the reactants are being used up (rate of reaction)
Quantity of reactants used/ time taken
Measuring how quickly the reactant is used up/ how quickly the product Is formed are 2 different ways to tell you the…
Rate of reaction
Equation to measure how quickly the product is formed (rate of reaction)
Quantity of product formed/ time taken
When measuring rate of reaction, what is the quantity (of reactant/ product) measured in
Grams or cm cubed
When measuring rate of reaction, what is time taken measured in
Seconds
Do reactions start of fast and slow down or slow and speed up
Start fast but slow down
(That’s why when measuring rate of reaction it’s only an average)
When drawing graphs showing rate of reaction, what goes on the x axis
Time (in seconds)
When drawing graphs showing rate of reaction what goes on the y axis
Mass of reactant used/ product formed (g or cm cubed)
5 factors affecting rate of reaction
Surface area
Temperature
Concentration
(Absence/ presence of) catalyst
Pressure of gases
What is meant by collision theory
In order to react, particles must collide with sufficient energy
Name for theory where in order to react, particles must collide with sufficient energy
Collision theory
The collision theory states that in order to… particles must…with sufficient…
React, collide, energy
Name for minimum amount of energy needed for particles to collide with each other and react
Activation energy
What is activation energy
Minimum amount of energy needed for particles to collide with each other and react
How temperature increases rate of reaction
As temperature increases, particles gain more kinetic energy and move faster so there are more frequent collisions and they will collide with more energy so more of the collisions are successful
Both concentration and pressure refer to how many particles there are per unit of…
Volume
How increasing pressure/ concentration increases rate of reaction
Increasing pressure/ concentration means that there are more particles per unit of volume so more frequent collisions which increases rate of reaction
How increasing surface area increases rate of reaction
The greater the surface area, the more particles there are that are exposed, so more frequent collisions which increases rate of reaction
What is a catalyst
Something that speeds up the rate of reaction without being used up
Why aren’t catalysts used in the reaction equation
They aren’t reactants or products
What do catalysts do to the activation energy
Lower it
(Particles need less energy to collide and react)
A catalyst provides an alternative… which lowers the activation energy reaction
Pathway
How to calculate rate of reaction at a particular time using graph
Draw tangent at particular time you’re interested in and measure gradient
When writing an equation what does the double arrow mean
The reaction is reversible
How to represent reaction being reversible when writing an equation
Use double arrow
(not single one)
In a reversible reaction we call the top arrow the… reaction
Forward
In a reversible reaction we call the bottom arrow the… reaction
Backward
True or false, in a reversible reaction both the forward and backward reaction can happen
True
True or false, in a reversible reaction the forward and backward reactions can take place at different rates
True
Dynamic equilibrium meaning
Point in reversible reaction where the forward and backward reaction are at the same rate in a closed system
(Both reactions are happening but they basically cancel each other out)
True or false, in dynamic equilibrium the amount of reactant and product are always equal
False
They are always constant but not necessarily the same as each other
Equilibrium can only be reached if the reaction is done in what type of system
Closed system
True or false, in a closed system no reactants or products can escape
True
True or false, at equilibrium the reactants are still turning into products and products still turning back into reactants
True- it’s just at the same rate so the amount of reactants and products are constant (not necessarily equal)
True or false, equilibrium can only be reached if the reaction is done in a closed system
True
Otherwise the reactants/ products could keep escaping
True or false, reversible reactions are always exothermic in one direction and endothermic in the other direction
True
Hydrated meaning
Water is present
Anhydrous meaning
No water is present
True or false, the position of equilibrium can change (shift to left/ right) depending on conditions
True
Le Chatelier’s principle is about the position of what during a reversible reaction
Equilibrium
3 main ways to change conditions of closed system
Temperature
Pressure
Concentration
If there are more reactants than products does the equilibrium lie to the left or right
Left
If there are more products than reactants does the equilibrium lie to the left or right
Right
Why do exothermic reactions have an overall negative energy change
Energy is released to surroundings so lost
Why do endothermic reactions have an overall positive energy change
Take in energy from surrounds so energy is gained (added)
What is a reversible reaction
Reaction where reactants can turn into products and products can turn back into reactants
What is meant by Le Chatelier’s principle
If a change is made to a system that’s at dynamic equilibrium, the system will try to undo (counteract) the change by favouring either the forward or reverse reaction so that it stays at dynamic equilibrium
If the concentration of the product is lowered, which reaction will the system favour and why
Forward reaction
Forward reaction turns reactants into products and the way to counteract a decreased product concentration is to increase it
If I increase the temperature what will the system do and how
Decrease temperature
Favour endothermic reaction which decreases temperature so moves towards endothermic
If I decrease the temperature what will the system do and how
Increase temperature by favouring (moving towards) exothermic reaction which increases temperature
If I increase concentration what will the system do
Decrease concentration by moving towards reaction that removes that chemical
If I decrease concentration what will the system do
Move towards reaction that produces that chemical
If I increase pressure what will the system do
Decrease pressure by favouring reaction that produces fewest molecules
If I decrease pressure what will the system do
Increase pressure by favouring reaction that produces greatest number of molecules
2 units for rate of reaction
g/s
Cm cubed/ s
(as the quantity of reactant used/ product formed can either be measured in grams or cm cubed and time is always in seconds)
5 examples of evidence for a chemical reaction occurring
Change in colour
Change in temperature
Bubbles/ fizzing
Precipitate (solid) formed
Odours/ sounds
What do particles do if they don’t have enough energy to react
Bounce off each other
Why does the rate of reaction decrease towards the end
Reactants becoming used up so less frequent collisions
How can we tell on a graph where the rate of reaction is highest
Steepest gradient
If the temperature of a reversible reaction is raised, what happens to the yield from the exothermic reaction
It decreases
