3 + 4 Rates of Reaction Flashcards
Define ‘rate of reaction.’
the change in concentration of a species per unit of time
State the two ways rate of reaction can be expressed for the single step reaction A → B.
Rate = -Δ[A] / Δt
OR
Rate = Δ[B] / Δt
State the units for any rate of reaction.
mol L-1 s-1 (or mol/l/s)
How can the rate of a reaction be calculated directly from a concentration-time graph?
by drawing a tangent and then calculating the gradient of it
When do reactions occur and which two conditions must be met in order for a reaction to occur?
reactions occur when particles collide
particles must possess at least a minimum amount of energy
particles must approach each other in a certain, relative orientation
Which two factors influence the reaction rate?
- the overall number of collisions occurring
2. the number of particles with enough energy to react
Define ‘activation energy, Ea.’
the minimum amount of energy required to initiate a chemical reaction
Define ‘transition state.’
highest energy point in the reaction
the configuration of the atoms at the time of the collision
On the following graph, label (1-4) reactants, products, ΔG and the transition state of the reaction.
1 - reactants
2 - products
3 - transition state
4 - ΔG
Draw out a normal Boltzmann distribution for a reaction.
see document
Explain how increasing temperature increases the rate of reaction.
particle speed increases so collisions are more frequent
particles have more energy, so can overcome the energy barrier
Draw out a normal Boltzmann distribution for a reaction and on the same axes draw another showing the effect of temperature on a rate of reaction.
see document
Explain how adding a catalyst increases the rate of reaction.
works by providing an alternative reaction pathway with a lower Ea
more particles now have the energy to react
Draw out a normal Boltzmann distribution for a reaction and on the same axes draw another showing the effect of a catalyst on a rate of reaction.
see document
Explain how increasing surface area of solid reagents/heterogeneous catalysts increases the rate of a reaction.
increases chances of a collision - more particles are exposed
powdered solids react quicker than large lumps
Explain how increasing the pressure of a gas increases the rate of a reaction.
forces gas particles closer together increasing the frequency of collision so the reaction rate increases
Explain how increasing the concentration of liquids increases the rate of a reaction.
the larger number of particles, therefore, more collisions
What does the rate of any reaction mainly depend on?
concentration of reactants
For the reaction equation, wA + xB → yC + zD, what is the general form of a rate equation?
Rate = k [A]^m [B]^n
where k = rate constant
m,n = reaction orders w.r.t to those reagents
m+n = overall reaction order
What is the only way a reaction order can be found?
by experiment
What is meant by a ‘zero-order’ of reaction?
where the rate is independent of the concentration of reactant
Rate = k
Overall order = 0
The rate does not change
What does a ‘zero-order’ reaction depend on?
depends on a catalytic bottleneck (catalyst)
What is meant by a ‘first-order’ of reaction?
where the rate is proportional to the concentration of a single reactant raised to the first (n^1) power
Rate = [A] k
overall reaction order = 1
How does integrated rate law describe the concentration of a reactant as a function of time?
ln[A]t = -kt + ln[A]0
y = mx+ b