c6 - rate of reaction Flashcards
How is rate of reaction calculated?
Rate of reaction (mol/s) = Moles of reactant used or product formed / time
Name three common ways of measuring rate of reaction
- Loss in mass of reactants
- Volume of gas produced
- Time for a solution to become opaque
Describe measuring the rate by monitoring mass
loss
Place the reaction flask on a balance
In these reactions (e.g. metal carbonate + acid) a gas is given off,
so record the decrease in mass in time intervals (note
hydrogen is too light).
Plot a graph of mass vs time
Describe measuring the rate by monitoring the volume of a
gas
Connect a gas syringe to a reaction flask and measure the volume of a gas
formed in time intervals. Plot a graph of volume vs time.
Describe measuring the rate by monitoring the
disappearance of a cross
Take a piece of paper and mark a cross (X) on it.
Put the reaction flask on this cross.
Mix the reagents, and measure how long it takes for a cloudy mixture to conceal a cross
State five factors affecting the
rate of a chemical reaction
- Concentration of reactants
- Pressure of gases (volume)
- Surface area
- Temperature
- Catalysts
What is the collision theory?
Chemical reactions can occur only when reacting particles collide with each other with sufficient energy (more than or equal to activation energy)
Describe and explain the effect of increasing temperature on the rate of reaction
As T increases, kinetic energy of particles increases, i.e. more energetic collisions
Also, they move faster, so they collide more frequently
Describe and explain the effect of increasing
concentration on the rate of reaction
Conc. increases = faster reaction,
More reactants = more frequent collisions
Describe and explain the effect
of increasing pressure of a gas
on the rate of reaction
It increases the number of gas molecules in the same volume and
so increases the frequency of collisions and therefore increases the rate of
reaction.
what is the relationship between pressure and volume
inversley proportional
Describe and explain the effect of increasing surface
area
Increasing the surface area of solid reactants increases the frequency of collisions
and so increases the rate of reaction
What is a catalyst?
A catalyst changes the rate of reaction but is not used up
what does a catalyst do
It increases rate of
reaction by providing a different pathway for the reaction that has a lower
activation energy.
what will the reaction profile look like for a catalyst reaction
a lower
maximum of the curve
what is an enzyme
An enzyme is a molecule that acts as a catalyst in a biological system
What is a reversible reaction?
A reversible reaction occurs when the products of a reaction can react backwards
to produce the original reactants
When is dynamic
equilibrium reached?
In a closed system, when the forward and reverse reactions occur at the same rate
and theconcentrations of reactants and products remain constant.
Describe Le Chatelier’s Principle
If a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteract change and restore the equilibrium.
Describe the effect of
lower the concentration of reactant
equilibrium will shift to the left (reactants)
to make more reactants
and oppose change
Describe the effect of
increasing temperature
equilibrium will shift to the left
favouring endothermic
to oppose change
Describe the effect of
increasing pressure
equilibrium position to shift towards the side with the smaller number of molecules
Describe the effect of a
catalyst on the position of the
equilibrium
No effect.
It just speeds up both forward and backward reactions equally.
if you lower the concentration of the products
equilibrium will shift to the left
to make more products
and oppose change
if you decrease temp
will shift to the right
favouring exothermic
and oppose change
if you decrease pressure
the equilibrium position to shift towards
the side with the larger number of molecules
