The Rate And Extent Of Chemical Change Flashcards
Rate of Reaction
- how fast the reactants are changed into products
- vary from iron rusting to explosions
How does the steepness of a graph show the rate of reaction
Steeper line, faster reaction
What does a flat line on a graph show?
The reaction has stopped
Collision Theory
- rate of reaction depends on collision frequency and energy transferred in each collision
- particles must have activation energy when they collide in order to react
- factors affecting rate of reaction must affect either collision energy or frequency
What four factors affect rate of reaction?
Temperature
Concentration of solution/pressure of gas
Surface area
Catalysts
How does increased temperature increase rate of reaction?
- particles all moving faster
- going to collide more frequently and with more energy
- more likely to have the activation energy and react
How does increasing concentration/pressure increase the rate of reaction?
- particles are more closely packed together
- collisions between particles are more frequent
How does increasing surface area increase the rate of reaction?
- more particles exposed
- more particles can react at once
- higher collision frequency
How do catalysts increase the rate of reaction?
- speeds up reaction without being used up itself
- dear ease activation energy required
Catalyst
Substance that increases the rate of a reaction without being used up
Experiment: magnesium and HCl rate of reaction
- set volume of HCl in conical flask
- add magnesium ribbon and attach gas syringe to flask
- start stopwatch; take gas readings at regular intervals
- plot results in a table
- plot graph (time on x-axis, volume of gas produced on y-axis)
Experiment: sodium thiosulphate and HCl rate of reaction
- both clear solutions: react to form a yellow precipitate of sulphur
- add set volume of dilute sodium thiosulphate to conical flask
- place flask on paper with a black cross drawn on it
- add dilute HCl and start the stopwatch
- time how long it takes for cross to disappear
Equilibrium
Both reactions are happening at the same rate
Reversible reactions
A + B <=> C + D
- concentrations of reactants fall, so backwards reaction speeds up and forwards reaction slows down
- eventually reach an equilibrium
- both reactions still happening with no overall effect
- equilibrium only reached in a closed system
Closed system
- none of the products/reactants can escape
- nothing else can get in
What conditions affect the position of equilibrium?
- temperature
- pressure
- concentration
Le Chatelier’s Principle
- change conditions of reversible reaction at equilibrium
- system tries to counteract the change
- predict the effect of changes made to a closed reaction system
How does a reversible reaction respond to changes in temperature?
- exothermic in one direction and endothermic in the other
- decrease temperature, equilibrium moves in exothermic direction to produce more heat and vice versa
- more products for exothermic reaction and vice versa
How does a reversible reaction respond to changes in pressure?
- only affects equilibrium involving gases
- increase pressure; equilibrium tries to reduce it
- moves towards direction where there are less molecules of gas
- vice versa
- balanced symbol equation used to see which side has more molecules of gas
How does a reversible reaction respond to changes in concentration?
- change concentration of reactants or products, system no longer in equilibrium
- system brings itself back to equilibrium
- increase concentration of reactants; system makes more products
- vice versa
What does a steep line show in a rate of reaction graph?
The reaction is happening very quickly
What two factors relating to collisions between particles influence the rate of reaction?
Collision Frequency
Energy of colliding particles
Equation used to calculate mean rate of reaction
RoR = products formed / time
OR
RoR = reactants used / time
Give three possible units for rate of reaction
Cm^3 / s
g / s
mol / s
