Topic C6 - Rates Of Reaction Flashcards
What is time usually measured in?
Seconds
What do flat lines show on a Rates of Reaction graph?
Reaction has finished
How can more product be formed?
By using more reactant
What do steep lines on a Rates Of Reaction graph show?
Faster rate of reaction
How can amount of product be measured?
1) Solids ~ grams (g)
2) Liquids/gases ~ cm cubed (cm^3)
3) Moles
What is the formula for MEAN RATE OF REACTION?
Either:
1)
Amount of product formed
——————————————-
Time
OR
2)
Amount of reactant used
——————————————-
Time
Units depend on what has been measured - they’re in the form AMOUNT / TIME
Common Units: g/s, cm^3/s, mol/s
Using Rate Graphs (Look at Book)
Step 1) Find the rate at a specific point by drawing a tangent to the curve at that point.
Change in Y
rate = gradient = ———————
Change in X
Step 2) Work out the mean rate over a period of time by calculating:
Overall change in Y ——————————————————-
Total time taken (change in X)
The rate of a chemical reaction depends on what?
1) Collision Frequency - more collisions between particles, faster rate of reaction. So doubling frequency collisions doubles the rate.
2) Collision Energy - enough energy needs to be transferred in a collision to overcome the activation energy and break the bonds to start the reaction.
What is ACTIVATION ENERGY?
The minimum energy, particles need to react.
Collision Theory
High Frequency
= High Energy
= Fast Reaction
Low Frequency
= Low Energy
= Slow Reaction
What happens to temperature during slow rate/fast rate of collisions?
Slow Rate = Low Energy = Cold
Fast Rate = High Energy = Hot (friction)
How does pressure or concentration affect rate of reaction?
Slow Rate
- Low Pressure
- Low Concentration
Fast Rate
- High Pressure
- High Concentration
More particles in the same volume - more frequent collisions
How does surface area affect rate of reaction?
More area for particles to collide with - more frequent collisions
Slow Rate
- Big Pieces of Particles
Fast Rate
- Small Pieces of Particles
The smaller the piece of the solid, the larger the surface area to volume ratio.
What do CATALYSTS do?
Speed up reactions by providing an alternative pathway for reaction.
Different reactions need different catalysts.
Enzymes are biological catalysts.
How does a CATALYST affect ACTIVATION ENERGY?
Lowers the amount of Activation Energy required.
What does REVERSIBLE REACTION mean?
Where the products can react to form the reactants again.
What is the only way equilibrium can be reached?
When a reversible reaction takes place in a closed system
Closed System -
where nothing can enter or leave
What is a CLOSED SYSTEM?
A system where nothing can enter or leave.
What happens to the concentrations of reactants and products at equilibrium?
The concentration of reactants and products stay the same/do not change.
What happens in a reversible reaction if there are more products than reactants?
The equilibrium lies to the right
What happens if there are more reactants than products in a reversible reaction?
The equilibrium lies to the left.
How can a change in reaction conditions affect a reversible reaction?
It can change the direction.
What does cooling the reaction do in a reversible reaction?
Favour the left side of the equation
Cause a backward reaction
What does heating the reaction do in a reversible reaction?
Favour the right side of the equation
Cause a forward reaction
If a reaction is endothermic in one direction of a reversible reaction what happens to the other?
It will be exothermic in the other
release heat energy
How much energy is transferred in a reversible reaction?
The same amount of energy is transferred in each direction
What is Le Chatelier’s Principle
If the conditions of a reversible reaction at equilibrium are changed, the system tries to counteract that change.
How does the system counteract change when a reversible reaction at equilibrium is changed? (Temperature)
Temperature:
1) Increases
2) Decreases
The equilibrium shifts favour to the…
1) endothermic direction to take in heat energy
2) exothermic direction to release heat energy
How does the system counteract change when a reversible reaction at equilibrium is changed? (Pressure)
Pressure:
1) Increases
2) Decreases
The equilibrium shifts to favour the…
1) side with fewer molecules of gas to reduce the pressure.
2) side with more molecules of gas to increase the pressure.
If a concentration of reactant is changed, the system will respond to reverse the change
If the concentration of:
1) Reactants increases
2) Reactants decreases
The system responds to:
1) Make more products
2) Make more reactants
