6.1 Rate of reaction Flashcards
What are the 2 equations for the mean rate of reaction? (2)
Rate of reaction = quantity of reactants used or products formed / time taken.
Rate of reaction = moles of reactant used or products formed / time taken.
What are the SI units for rate of reaction? (3)
Rate of reaction: g/s | cm3/s | mol/s
Quantity: g | cm3 | mol
Time: s
How do you find the rate of reaction graphically? (1)
Draw tangent to curve at specific point to calculate gradient.
List what the 5 factors that affect rate of reaction are? (5)
- Concentration
- Pressure
- Surface area
- Temperature
- Catalysts
What is the collision theory? (1)
Chemical reactions can only occur if reacting particles collide with each other with sufficient energy.
What is the activation energy? (1)
The minimum amount fo energy particles require to react.
Describe what happens when you increase the concentration of reactants in solution, pressure of reacting gases or surface area of solid reactants? (2)
1) Frequency of collisions increase,
2) So rate of reacting increases.
Describe what happens when you increase the temperature of a solution/substance?
1) Frequency of collisions increase,
2) So collisions become more energised,
3) So rate of reaction increases.
Describe what two things can happen when a catalyst is added to a solution? (2)
1) Decrease activation energy needed so less energy needed for reaction to take place.
2) Provide different pathway for chemical reaction with lower activation energy.
What is a reversible reaction? (1)
When the products of a reaction can react to produce the original reactants (⇌)
What circumstance causes change to the direction of a reversible reaction? (1)
Conditions - forward reaction uses hot conditions, backwards reactions use cold conditions.
If a reversible reaction is exothermic one way, what is it in the opposite direction?
Endothermic.
What amount of energy is transferred in a reversible reaction in each direction? (1)
The same amount - one will have energy that is lost whilst the other will have the same amount of energy which is gained.
What 2 things are needed for equilibrium to occur in a reversible reaction? (2)
- Closed system.
- Rate of reaction in both directions are the same.
The relative amount of all reacting substances at equilibrium is what? (1)
Dependent on the conditions of the reaction.
What are the effects of changing conditions on equilibrium? (1)
When a system is at equilibrium and a change occurs to any condition, the system responds to counteract the change (Le Chatelier’s principle)
What is the effect of changing concentration on equilibrium? (2)
If one of product’s or reactant’s concentration changes, the concentrations of all substances will change until equilibrium is reached.
- ↑concentration of reactants: equilibrium shifts to products so more products is produced until equilibrium is reached again.
- ↑ concentration of products: same as reactants but equilibrium shifts to reactants.
What are the 2 effects temperature changes have on equilibrium? (2)
- ↑temperature: equilibrium shifts in direction, and increases the yield of, the endothermic reaction.
- ↓temperature: equilibrium moves in direction, and increases yield of, the exothermic reaction.
What are the 2 effects pressure changes have on equilibrium? (2)
- ↑pressure: equilibrium shifts to side of equation with fewer moles of gas, increasing its yield (e.g. N2+3H2 ⇌ 2NH3 - left side has more moles (3+1=4) than right (2) so equilibrium shifts to right).
- ↓pressure: equilibrium shifts to side of equation with more moles of gas, increasing its yield (for previous example, equilibrium would move left, producing more reactants)
What effect does a catalyst have on equilibrium position? (1)
No effect - speeds reaction on both sides equally.
