Rate and Equilibria A2 Flashcards
Also revise calculations like finding units and RICE tables
What are the units of rate?
Mol dm^-3 s^-1
On a conc-time graph, what does the gradient represent?
Rate of reaction
On a rate-conc graph, what is the shape and direction of the line for a zero, first and second order reaction?
Zero = straight horizontal line
First = straight positive line (directly proportional)
Second = curved positive line
How does a zero, first and second order reactant affect rate if its concentration is doubled?
Zero = no effect
First = doubles if doubled
Second = quadruples if doubled
What reactants are shown in the rate equation? and how?
Zero order - not shown.
First order and second order are shown.
The order of a specific reactant is the power to which the concentration of the reactant is given.
What is K? What is the only thing that affects it?
Rate constant.
Temperature
How do you calculate the overall order of reaction?
Sum all the orders of the reactants.
How are orders of reactions found?
Experimentally
Give three methods of monitoring the rate of a reaction.
Mass loss, gas collection and colorimetry
Describe the conc-time graphs for zero, first and second order reactions
Zero = straight negative line
First = curved negative line - constant half life
Second = (more) curved negative line
What is the equation linking first order k and half-life?
k = ln2 / half-life
what is a clock reaction?
The time taken for a visual change in a reaction - generally measured by a colorimeter.
What is the rate determining step?
The slowest step in a reaction / mechanism
What is the link between the rate equation and RDS?
Rate equation only includes species up to and in the RDS.
What equation links the rate constant and activation energy?
Arrhenius equation - (ln k = ln A - Ea/RT)
On a graph of ln k against 1/T what does the gradient give you?
-Ea/R
On a graph of ln k against 1/T what does the y-intercept give you?
ln A
In the Arrhenius equation, what is R and A?
R = gas constant (8.31 J mol^-1 K^-1)
A = Arrhenius constant
How can you work out activation energy from a ln k against 1/T graph?
look at Arrhenius equation as if y=mx+c
y = ln K
m = -Ea/R
x = 1/T
C = ln A
Rearrange m so Ea = m x -R
How do you figure out A from y-intercept on 1/T against ln k graph?
A = e^y-intercept
What is the name for equilibrium when all the species have the same state? And different state?
What state species does the Kc expression include?
Same states = homogeneous equilibrium
Different states = heterogeneous equilibrium
Only includes aqueous or gases.
What method do you use to find the moles of species at equilibrium?
RICE tables
Reaction, Initial moles, Change in moles, Equilibrium moles
Moles/volume to calculate concentration at equilibrium.
How do you calculate partial pressures?
From moles at equilibrium (RICE table) calculate mole fraction (mol of substance / total moles).
Multiply total pressure by mole fraction to calculate partial pressure.
How do you write expression for Kp? What are the units?
p(C) / p(A) p(B)^2 - example
Always p and curved brackets
Generally, units are Pa or atm
How does temperature affect K?
Exothermic reactions: Increasing temperature decreases K
Endothermic reactions: Increasing temperature increases K
What happens to equilibrium position if temperature increases for an exothermic reaction? Explain why.
Equilibrium shift to the left.
K decreases so ratio of product:reactant is greater than Kc. So reactants must increase and products decrease so shift to the left.
What happens to equilibrium position if temperature increases for an endothermic reaction? Explain why.
Equilibrium shift to the right.
K increases so ratio of product:reactant is smaller than Kc. So reactants much decrease and products increase so shift to the right.
How does altering concentration and pressure effect K?
Does not affect K.
But does affect equilibrium position as concentrations/pressures must change accordingly.
How does increasing concentration of reactant affect equilibrium position?
Kc remains constant but ratio is smaller than Kc (as reactants on bottom of fraction). So to maintain Kc value, reactant must decrease and product must increase so equilibrium shifts to the right until ratio = Kc.
How does increasing pressure affect equilibrium position?
Kp remains constant but each partial pressure increases, so ratio is greater than Kp. So p(reactant) must increase and p(product) must decrease so equilibrium shifts to the left until ratio = Kp.
Acception = when you have p()^2 involved
