C6- Rate And Extent Of Chemical Change Flashcards
What is rate of chemical reaction
How fast reactants are changed into products
Examples of rates of reaction
Slowest - rusting of iron
Medium - metal magnesium reacting with acid to produce bubbles
Quick - burning (explosions faster)
Describe graphs for rates of reactions
Find reaction speed by recording amount of product formed or reactant used over time
Steeped line = faster rate of reaction
Overtime steepness decreases as reactant used up
Quickest reactions have steepest lines and flatten out quickest
What must particles collide with in order to react
The activation energy
What’s activation energy
Minimum energy required during collision of particles for them to react
What does the rate of reaction depend on
Collision frequency of reacting particles - more collisions = faster reaction rate
Energy transferred during collision - collide with enough energy for successful reaction
How does temperature affect rate of reaction
Temp increase = particles move faster
Collide more frequently which increases rate
Faster = more energy = more successful collisions
How does concentration/pressure affect rate of reaction
Solution more concentrated = more particles knocking in same volume = collisions more frequent
Pressure increase = same particles in smaller space
How does surface area increase rate of reaction
If reactant is solid, breaking into smaller pieces will increase SA to V ratio - same volume of solid , particles have more space = more collisions.
How does a catalyst affect the rate of reaction
Different catalysts for different reactions
Catalysts decreases activation energy - provide alternate reaction pathway with lower activation energy.
Enzymes are biological catalysts - catalyse reactions I’m living things
Equation for rate of reaction
Rate of reaction = amount of reactant used or product formed/time
How does precipitation and colour change measure rate of reactions
Record visual changes - initial solution transparent and product is precipitate which clouds solution
Observe mark through solution and see how long it takes for it to disappear - can’t plot ROR graph
How does change in mass measure rate of reaction
Measuring speed of reaction that produces a gas carried out with mass balance - as gas released, mass disappears on mass balance
Quicker reading drops = quicker reaction - most accurate but releases gas into room
How is Volume of gas given off a measure of rate of reactions
Gas syringe to measure volume of gas given off - more gas given off = faster reaction
Syringe gives volume accurate to cm3
Measurements at regular intervals and plot ROR graph
Equation to work out mean rate of reaction
Mean rate = change in y / change in x
How do you find reaction rate at a specific point
Draw a tangent and find tangents gradient - rise/run
What will reversible reactions reach
Will reach equilibrium
What happens as reactants react
Their concentrations fall - forward reaction will slow down
What happens as more products are made…
concentration rises and backwards reaction speeds up
After a while, the forward reaction will go at the same rate as the backward one - equilibrium
What’s the forward and backward reaction
Forward: A-> ———-\ C >
B -> forward D>
Backward < A \———
What happens at equilibrium
Both reactions are still happening, but there’s no overall effect > concentrations of reactants and products have balanced and won’t change
Equilibrium only reached if…
Reversible reaction takes place in a closed system
What does reactions at equilibrium not mean
Doesn’t mean amount of reactants and products are equal
What happens if equilibrium is to the right or left
To the right - product concentration greater than reactants
To the left - reactant concentration greater than products
What does the equilibrium position depend on
Temperature, pressure, concentration
E.g heating an equilibrium may cause a position change
In reversible reactions, if reaction is Exothermic in one direction…
It will be endothermic in the other direction
Energy transferred from surroundings by endothermic reaction is equal to….
Energy transferred to surroundings during exothermic reactions
What is the Le Chateliers principle
Idea that if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract that change
Changes to temperature in equilibrium
If you decrease the temperature, equilibrium will move in exothermic direction to produce more heat
More products for exothermic reaction and fewer products for endothermic reaction
Pressure changes in equilibrium
Increase pressure, equilibrium tries to reduce it - move in direction of fewer molecules
Decrease pressure, more in direction of more molecules
Balanced symbol equation to see which side has more gas moles
Change of concentration in equilibrium
Increase concentration of reactants - system tries to decrease by making more products
Decrease concentration of products - reduce amount of reactants etc
