Rates & Equilibrium Flashcards
RATE OF REACTION
Change in concentration of a reactant or product with time.
ORDER, m
The order with respect to a reactant is the power to which the concentration of the reactant is raised in the rate equation.
RATE CONSTANT, k
The constant that links the rate of reaction with the concentrations of the reactants raised to the powers of their orders in the rate equation.
HALF-LIFE
The time taken for the concentration of the reactant to reduce by half.
RATE DETERMINING STEP
The slowest step in the reaction mechanism of a multi-step reaction.
• If a reactant appears in the rate equation, it must also appear in the rate determining step
• The order with respect to the reactant tells you how many particles of the reactant are involved in the rate determining step.
Zero Order Graphs
Rate-Concentration Graph:
• horizontal line parallel to x-axis
• rate is constant
Concentration-Time Graph:
• straight diagonal line going down, with a negative gradient
• half-life decreases with time
First Order Graphs
Rate-Concentration Graph:
• straight line through 0,0, going up, with a positive gradient
Concentration-Time Graph:
• curve sloping down
• constant half-life
Second Order Graphs
Rate-Concentration Graph:
• curve sloping up, starting at 0,0
Concentration-Time Graph:
• curve sloping down
• half-life increases with time
What can be said about the half-life of a first-order reaction?
It is independent of the concentration
How can a concentration-time graph be used to determine the rate of reaction at a given time, (t=0)?
- Drawing a tangent to the curve at time, t.
* Finding the gradient of the tangent to the curve
Effect of temperature change on rate constant (k) and rate of reaction
If the temperature of a reaction is increased then the rate constant k increases and hence the rate of a reaction also increases
Effect of concentration on half life in 1st order reactions
No effect
Effect of temperature increase on equilibrium
Equilibrium shifts in the endothermic direction
Effect of temperature increase on Kc
In endothermic reaction- Kc increases
In exothermic reaction- Kc decreases
Effect of pressure on equilibrium
Shifts in the direction of the side with fewer gaseous moles.
Effect of pressure on Kc
No effect
Effect of changing concentration on Kc
No effect
Effect of changing concentration on equilibrium
Shifts in direction where conc has been minimised until equilibrium is achieved again
Effect of catalyst on Kc and equilibrium
No effect Rate of reaction increases in both directions
LE CHATELIER’S PRINCIPLE
When a system in dynamic equilibrium is subjected to a change, the equilibrium position will shift to minimise the change.
Equilibrium
- rate of forward reaction=rate of reverse reaction
* concentration of reactants and products remain constant
Kc >10¹⁰
Very much to RHS
Kc >10² (100)
Just to RHS
Kc Approximately 1
In the middle
Kc below 10² (100)
Just to LHS
Kc above 10¹⁰
Very much to LHS
How could you use the results from various experiments to show the order with respect to the reactants of a reaction.
- vary one reactant whilst keeping the other constant
- repeat the other way round
- Calculate rate, rate=conc/time
- Relate order to rate/time graph
Explain why it is difficult to predict how the yield of a reactant will change.
- Increasing/decreasing temp would have this effect…
- However increasing/decreasing pressure would…
- Relative effect of temp and pressure are unknown - don’t know which has biggest effect
