Reaction profiles

Question 1

energy profile diagrams

Answer 1

model energy changes that happen during reactions

Question 2

Describe the reaction profile for a typical exothermic reaction

Answer 2

-reactants start out with a higher level of energy

-energy increases until the activation energy
(a short amount because less energy is released from breaking bonds)

-energy then decreases until it reaches a low level
(making bonds takes more energy)

-the products end with a lower level of energy

Question 3

energy change in a reaction

Answer 3

change from the starting energy to the final energy level

Question 4

characteristics of an exothermic reaction profile

Answer 4

• energy level of reactants is greater than the energy level of the products
• energy change of the reaction is negative (energy transferred to the surroundings)

Question 5

activation energy

Answer 5

minimum energy needed to start a reaction/break the bonds in the reactant particles

Question 6

How can activation energy be supplied?

Answer 6

• (continually) heating the reaction mixture
• applying a flame or a spark
• passing an electric current though an electrolyte

Question 7

Describe the reaction profile for a typical endothermic reaction

Answer 7

-reactants start with a lower level of energy

-the energy gradually increases a significant amount to the activation energy
(breaking bonds releases a lot of energy)

-energy then decreases slightly
(making bonds requires less energy)

-products have a higher level of energy than the reactants

Question 8

characteristics of an endothermic reaction profile

Answer 8

-energy level of the reactants is lower than energy level of the products

-energy change of the reaction is positive
(energy is transferred from the surroudings)

Question 9

What does the energy change in a reaction profile represent?

Answer 9

the activation energy

Question 10

What effect does a catalyst have on a reaction profile?

Answer 10

lower activation energy/lesser energy change

Question 11

Describe the features of a reaction profile graph

Answer 11

• energy on the y axis
• progess of reaction on the x axis
• reactants labelled at start
• products labelled at end

-activation energy labelled
(from start energy to the top of the curve)

-energy change labelled
(from start energy to end energy)

Question 12

Sketch reaction profiles for the following reactions:

a) CH4 + 2O2 -> CO2 + 2H2O (exothermic)
b) CaCO3 -> CaO + CO2 (endothermic)

Answer 12

correct axises (y: energy, x: progress of reaction/time)
correct shape (net negative energy change)
reactants and products identified/labelled
activation energy identified
energy change identified