Topic 9: Reaction Kinetics

Q/A for Edexcel new specification (2016) Chemistry. I also have some quizzes for other topics available.

HideShow resource information
  • Created by: LouiseG
  • Created on: 27-04-16 09:11
How do you find a rate of reaction graphically from a concentration/time graph?
Draw a tangent to the time under investigation and calculate its gradient.
1 of 17
Why, if a particle makes 10^9 collisions per second, are reactions not immediate?
The collisions do not always result in a reaction. The molecules need to collide with enough energy (the activation energy) and with the correct orientation (with minimum steric hindrance)
2 of 17
When CH3Cl is heated under reflux, with NaOH, substitution of the chlorine occurs, forming methanol. Why does this not occur with CCl4?
The four chlorine atoms are sufficiently large enough to prevent the nucelophile approaching the C(d+) atom, so substitution doesn't occur. This is steric hinderance. (Whereas, in CH3Cl, the H atoms are much smaller).
3 of 17
Why will 2M HCl form CO2 when reacting with CaCO3 more quickly than 0.5M HCl?
Higher concentrations increase the rate of reaction, as there are more collisions in the same volume and particles are closer together.
4 of 17
What is the effect of increasing pressure on a reaction?
It will increase the rate (for a gas phase reaction), for similar reasons to an increase in concentrations. There will be no affect on solid and liquid phase reactions.
5 of 17
Why will a powdered MnO2 catalyst catalyse a reaction faster than larger solid pieces?
The powder has a higher surface area, therefore a larger area for particles to be absorbed and reaction on the catalyst surface.
6 of 17
What are the axes on the Maxwell-Boltzmann curve?
Fraction of molecules with Energy E(y) and Energy E (x)
7 of 17
What is the peak on the Maxwell-Boltzmann distribution curve?
The most probable energy of particles (NOT the average energy)
8 of 17
What is the area under the curve?
The number of particles/molecules
9 of 17
Why does the curve start at the origin and approach the x-axis asymptotically?
It starts at the origin as no particles have no energy, and cannot cross the x axis as there cannot be a defined "maximum energy" for the particles
10 of 17
What happens to the curve if the temperature is raised?
Th peak moves down and to the right. A greater proportion of molecules have the activation energy to react, which increases the rate.
11 of 17
What is a "solvent cage"?
When particles of a solute are surrounded by the solvent, trapping them together and encouraging an increased rate of reaction .
12 of 17
What will the addition of a catalyst do to a Maxwell-Boltzmann curve?
Nothing to its shape. However, it will decrease the activation energy (shifts to the left on the curve) as it provides an alternative reaction pathway.
13 of 17
What does a reaction profile diagram show?
The relative energy of reactants and products, but also the activation energy (the "bump" - NOT shown on enthalpy LEVEL diagrams)
14 of 17
What is a heterogeneous catalyst?
A catalyst in a different phase to the reactants. (A "phase" is not the same as "state", for example two immiscible liquids are in different phases but not different states.)
15 of 17
Name two heterogenous catalysts commonly used in industry.
Vanadium (V) Oxide (Contact process) and iron (Haber process)
16 of 17
What do catalysts do to the activation energy "hill" in a reaction profile diagram?
It reduces in height. Note the positions of the products and reactants energy levels do not change
17 of 17

Other cards in this set

Card 2

Front

Why, if a particle makes 10^9 collisions per second, are reactions not immediate?

Back

The collisions do not always result in a reaction. The molecules need to collide with enough energy (the activation energy) and with the correct orientation (with minimum steric hindrance)

Card 3

Front

When CH3Cl is heated under reflux, with NaOH, substitution of the chlorine occurs, forming methanol. Why does this not occur with CCl4?

Back

Preview of the front of card 3

Card 4

Front

Why will 2M HCl form CO2 when reacting with CaCO3 more quickly than 0.5M HCl?

Back

Preview of the front of card 4

Card 5

Front

What is the effect of increasing pressure on a reaction?

Back

Preview of the front of card 5
View more cards

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all Energetics resources »