Chapter 10 - Reaction Rates and Equilibrium Flashcards
What is meant by rate of reaction?
How fast a reactant is used up or how fast a product is formed
What is the equation for rate of reaction?
Change in concentration/time
What does the gradient of the curve in a concentration-time graph tell us?
The rate of the reaction
Describe shape of the curve as the reaction progresses
Becomes less steep
Reactants are being used up as their concentrations decrease
Describe the shape of the curve at the start of the reaction
Slope is steepest
Rate is fastest
Each reactant is at its highest concentration
Describe the shape of the curve once one of the reactants has been completely used up
Flattens/plateaus
What are some factors which can affect the rate of a chemical reaction?
Concentration (or pressure when reactants are gases)
Temperature
Use of a catalyst
Surface area of solid reactants
What must the reactant particles do in order for a reaction to occur?
Must come together and collide with the correct orientation
Energy greater than the activation energy, for the reaction
Why does the rate of reaction increase as the concentration of a reactant increases?
More particles in a given volume
So more frequent collisions
Therefore faster rate of reaction
What happens so the rate of reaction when a gas is compressed into a smaller volume?
Increases
Pressure of gas increases
Gas molecules are close together and collide more frequently
What are the methods for following the progress of a reaction?
Monitoring the removal (decrease in conc.) of a reactant
Following the formation (increase in conc.) of a product
How do we monitor the rate of reaction by collecting gas?
Use a gas syringe
Record gas volume at time intervals i.e. every 10s
What is a catalyst?
Is a substance that increases the rate of a reaction of a chemical reaction without undergoing any permanent change itself
Not used up
May react with reactant to form an intermediate or provide surface
Always regenerated at the end
What does a catalyst do?
Provides an alternative reaction pathway with a lower activation energy
What is meant by a homogeneous catalyst?
Has the same physical state as the reactants
What is meant by a heterogeneous catalyst?
Has a different physical state from the reactants
What does adsorption mean?
When the reactant molecules form weak bonds with the catalyst surface
What does desorption mean?
When product molecules leave the catalyst surface
What do catalysts do in terms of temperature and how does this link to combustion?
Lowers the temperature needed for the reaction
Means less electricity from combustion of fossil fuels is used
Less combustion of fossil fuels results in a reduction of CO₂ emissions
What does the Boltzmann distribution curve show?
The spread of molecular energies in a sample of gas molecules
What does the area under the Boltzmann curve show?
Equals the total number of molecules
What does the shaded area in a Boltzmann curve show?
Shows the proportion of molecules with an energy greater than the activation energy
What is the relationship between the Boltzmann curve and the x-axis?
The curve does not meet the x-axis
There is no maximum energy for a molecule
What happens to the Boltzmann distribution curve at higher temperatures?
At higher temperature, T₂, the peak is lower and shifted to the RIGHT
At higher temperature, T₂, a greater proportion of molecules have an energy greater than the activation energy
