Chapter 10 Flashcards
How does concentration/ pressure affect the rate of reaction?
- The higher the concentration/ pressure, the more molecules per unit volume, which increases the frequency of collisions
What are 3 ways of monitoring the rate of reaction of reactions that produce gas?
- Use a gas syringe to measure the volume of gas produced
- Place the conical flask (with wool at the top to prevent any splashing) on a balance, and record the change in mass
- Use an inverted measuring cylinder and trough filled with water, and record the volume of displaced water
How is rate of reaction usually shown on a graph?
- Time (s) against concentration/ mass/ volume of gas, etc.
- The rate of reaction is the gradient
What do catalysts do?
- A catalyst provides an alternative reaction route with a lower activation energy
- This causes a greater proportion of the molecules to have the activation energy or more
- This increases the rate of the reaction
- They themselves are not used up
What needs to be included on an enthalpy profile (including the use of a catalyst)?
- x-axis: progress of reaction
- y-axis: enthalpy
- ΔH
- Ea
- Ec
What is a heterogeneous catalyst?
- A catalyst that has a different physical state from the reactants
What is a homogeneous catalyst?
- A catalyst that has the same physical state as the reactants
What are 2 benefits of using a catalyst?
- Lower temperatures and pressures can be used
- This decreases the combustion of fossil fuels and therefore carbon dioxide emissions
What does the Boltzmann distribution show?
- The spread of molecular energies in gases
When drawing the Boltzmann distribution, what are 7 things to include?
- x-axis: energy
- y-axis: number of molecules
- Starts at origin
- Peak
- Lower gradient on right
- Ea
- Does not meet x-axis at the end of
Why does the graph cross at the origin?
- None of the molecules have 0 energy
What does the area under the graph show?
- The total number of molecules
Why does the curve never meet the x-axis?
- There is no maximum energy of a molecule- the curve would need to reach infinite energy for it to meet the x-axis
How does temperature affect a Boltzmann distribution curve?
- The peak is lower and to the right
- The curve still has a higher gradient on the left side rather than the right side, and the Ea is in the same position
- The area under the curve is the same
How does increasing the temperature increase the rate of reaction?
- At higher temperatures, more molecules have energy greater than or equal to the activation energy