Chapter 10 Rates of Reaction and Equilibrium Flashcards
What is meant by rate of reaction
- How fast a reactant is used up
- How fast a product is formed
What is the equation for rate of reaction
Change in concentration / Time
Describe and explain the curve on a concentration-time graph
- Here the slope is steepest – the rate is fastest at the start of the reaction (each reactant is at its highest concentration)
- The curve becomes less steep as the reaction
progresses – the reactants are being used up and their concentrations decrease - Eventually the curve becomes a straight line parallel to the x-axis – the reaction is complete (one of the reactants has been completely used up)
What does the gradient of a curve on a concentration-time graph
The rate of reaction
What factors affect rate of reaction
- concentration (or pressure when reactants are gases)
- temperature
- use of a catalyst
- surface area of solid reactants
What is the collision theory
For a reaction to occur reactant particles must come together and
collide with:
* The correct orientation
* Energy greater than the activation energy, Ea for the reaction
Why is there a slower rate of reaction at lower concentrations
Less particles in a given volume so less frequent collisions and therefore slower rate of reaction
Why is there a faster rate of reaction at a higher concentration
More particles in a given volume so more frequent collisions and
therefore faster rate of reaction
Why is there a faster rate of reaction when gas is compressed into a smaller volume
Gas molecules are closer together and
collide more frequently
How can you measure the progress of a reaction
- Monitor the removal of a reactant
- Monitor the formation of a product
What is a catalyst
A substance that increases the rate of a chemical reaction without undergoing any permanent change itself
What does a catalyst do
A catalyst provides an alternative reaction
pathway with a lower activation energy
What is a Homogeneous Catalyst
A catalyst that has the same physical state as the reactants
What is a heterogeneous catalyst
A heterogeneous catalyst has a different physical state from the reactants.
How does a Heterogeneous Catalyst work
- The reactant molecules form weak bonds with the catalyst surface - absorbtion
- Bonds within the molecules break
- New bonds form
- Product molecules leave the catalyst surface - desorbtion
How do Catalysts have a sustainability and economic importance
- Catalysts lower activation energy
- This lowers the temperature needed for the reaction
- Lower temperatures mean less electricity from combustion of
fossil fuels is used
Less combustion of fossil fuels results in a reduction emissions from atmospheric pollutants.
What does the Boltzmann distribution curve show
The Boltzmann distribution curve shows the spread of molecular energies in a sample of gas molecules
How does the boltzman distribution curve change at a higher temperature
At higher temperature, the peak is lower and
shifted to the right
How does the boltzman distribution curve change with a catalyst
A greater proportion of molecules exceed the new activation menergy
What is equillibrium
- The rate of the foward reaction is equal to the rate of the reverse reaction
- The concentrations of reactants and products remain constant
If you increase the concentration of reactants, which way does equilibrium shift
Equilibrium shifts to the right
If pressure is increased, which side of the reaction will be favoured
equilibrium position moves to the side with fewer gaseous molecules
How does a catalyst affect equilibrium
A catalyst does not affect the
position of equilibrium
What is the equation for the equilibrium constant
For the equation:
aA + bB –> cC + dD
Kc = [C]c[D]d / [A]a[B]b
What does Kc tell you
On which side of the equation the position of
equilibrium lies.
Where does equilibrium lie if Kc = 1
Equilibrium lies halfway between the reactants and products
[reactants] = [products]
Where does equilibrium lie if Kc > 1
Equilibrium lies on the right of the equation
[products] > [reactants]
The larger the value of Kc the further to the right equilibrium lies
Where does equilibrium lie if Kc < 1
Equilibrium lies on the left of
the equation
[reactants] > [products]
