Block 3: Kinetics Flashcards
What is the rate of a chemical reaction?
The change in concentration per unit time (usually mol L-1 s-1)
What is the rate of a reaction equation?
Rate = - 1/a x (delta [A]/ delta t)
A= reactant a
What factors affect the rate of reaction?
- the nature of the reaction (eg metallic sodium reacts with O2 to form oxide fast, iron= slowly, gold= not at all)
- concentration of reactants
- the temperature
- physical state of reactants (eg powder = larger surface area= fast)
- presence of catalysts
- action of light
How is the instantaneous rate of many reactors related to the concentration of reactants?
By a rate law
What is a first order reaction and what does it mean?
The rate is directly proportional to the concentration of the reactant; if the concentration is doubled, the rate doubles
What is a second order reaction and what does it mean?
The rate is proportional to the square of the concentration; if the concentration of the reactant is doubled, the rate increases by a factor of 4
Equation for first order reaction?
Rate {proportional to} [A]
Equation for a second order reaction?
Rate {proportional to} [A]^2
What is a zero order reaction?
Where rate is independent of concentration
What is a third order reaction?
Where rate is proportional to the cube of a concentration
What is an instantaneous rate?
Rate at a particular time during the course of reaction and is the same as the slope
What happens to the rate if you have more than one reactant concentration?
It’s proportional to both;
Rate {proportional to} [A] x [B]
What is the proportionality constant? What, therefore, is the reaction?
The rate constant, or “k”
Therefore; rate = k [A] x [B]
What’s the initial rate?
The change in concentration
How do we work out the units?
By balancing the rate units/the concentration^2
What are the units of a first order rare constant?
S-1
What’s the concentration of zero order rate reaction?
Mol L-1 s-1
What happens as order increases?
Rates become slower
How would you rearrange
Rate= k[A][B]^2 to find the k value?
K = rate / [A][B]^2
What is an integrated first order rate law equation?
[R] = [R]oe^-kt
R= conc of reactant after time Ro= conc of reactant at start t= time in seconds
What’s the integrated form of a second order reaction? (Reactants to products)
1/[R] = 1/[R]o + kt
Does the first order plot of integrated law rate make a straight line?
Yes
Does the second order graph of integrated law make a straight line?
No, it’s curved
What is the half-life of a reactant?
The time it takes for a reaction to fall to half of its initial value, denoted by symbol t 1/2
