5.1 - 5.3 + 18.1 - 18.5 Kinetics Flashcards
Explain collision theory
For a reaction to take place particles must collide with enough energy and in the correct orientation. This is called a successful collision.
Define activation energy, Ea
The minimum amount of energy required to start a reaction
What are 3 reasons might there be for a collision between reactant particles not leading to a reaction?
- They do not collide with enough energy
- They are not in the correct orientation
- The collision was not between the correct particles
What does a Maxwell-Boltzmann distribution graph show?
The different amounts of energy that particles in a given gas or liquid have
Define rate of reaction
The change in concentration of a substance per unit time
List 4 things that can have an effect on the rate of reaction
- The concentration or pressure
- The surface area
- The temperature
- Adding a catalyst
Why does an increase in concentration or pressure increase the rate of reaction?
More particles in a given volume so more frequent successful collisions will happen
Why does an increase in surface area increase the rate of reaction?
More particles of solid exposed so more chance of a successful collision with other reactant particles
Why does an increase in temperature increase the rate of reaction?
- Particles move faster so collide more often
- More particles with more energy than the activation energy
Why does adding a catalyst increase the rate of reaction?
Catalyst provides an alternative reaction pathway with a lower activation energy. Lowering the activation energy means more particles with have energy exceeding the activation energy so more successful collisions will happen.
List three ways of measuring the rate of reaction
- If a gas is produced, measure volume produced or mass lost over time
- Precipitation/colour change
- Changes in electrical conductivity or pH
What is the effect of increase in rate on increase in concentration if the reactant is first order?
Increase in rate = Increase in concentration
What is the effect of increase in rate on increase in concentration if the reactant is second order?
Increase in rate = (Increase in concentration)²
What is the effect of increase in rate on increase in concentration if the reactant is zero order?
Increase in concentration has no effect on rate
What is the rate equation?
rate = k [A]x^ [B]y^
k = rate constant [ ] = concentration x = order with respect to A y = order with respect to B (x+y) = overall order of reaction
Describe what a graph showing zero order would look like
Concentration vs time:
- A straight line of constant decline
Rate vs concentration:
- A straight horizontal line
Describe what a graph showing first order would look like
Concentration vs time:
- A slightly sloping declining curve with a constant half-life
Rate vs concentration:
- A straight line diagonally up
Describe what a graph showing second order would look like
Concentration vs time:
- A steeply declining curve that then levels out
Rate vs concentration:
- A line curving up
Rate vs concentration²:
- A straight line diagonally up
What is the rate constant, k?
The value of the rate at any particular temperature when the concentration of all species in the rate equation are 1 mol dm⁻³
Bigger k = Faster reaction
Describe the link between the rate constant and activation energy
As Ea↑, rate ↓ so k↓
Describe the link between the rate constant and temperature
As temp↑, rate ↑ so k↑
What do the different parts of the Arrhenius equation stand for?
k = rate constant A = Arrhenius constant e = mathematical quantity, e Ea = Activation energy (J mol⁻¹) R = Gas constant (8.31 J k⁻¹ mol) T = temp (k)
What is the conversion for °C to K?
°C + 273 = K
On a graph of lnk against 1/T, what does the gradient represent?
Gradient = -Ea/R
Y-intercept = lnA
Explain why using a large excess of all other reactants means the rate of reaction depends only on the one not in excess
- The concentration of the reactants in excess is effectively constant
- This means these reactants become zero order
What must be done to a solution of reactants before the concentration of one of them is measured?
- Stop the reaction
- By cooling
rate = k[E]
Why would doubling the temp have a much greater effect on rate of reaction than doubling [E]?
- Reaction occurs when molecules have E>Ea
- Doubling T may cause many more molecules to have E>Ea
- Doubling [E] will only double molecules with E>Ea
What effect does introducing a catalyst have on a Maxwell-Boltzmann distribution curve?
No effect
Give the logarithmic arrhenius equation
lnK = (-Ea/R) x (1/T) + lnA
