Bond Energies

Question 1

What do energy levels show?

Answer 1

Whether the reaction is endo-/exothermic

Question 2

Describe and exothermic bond energy diagram

Answer 2

The products are LOWER than the reactants. The difference in height = the energy given out in the reaction (per mole)
ΔT is negative here.
The initial rise in the line = the energy needed to break the old bonds = activation energy
(From 10 to 5 on a clock, clockwise)

Question 3

Describe and endothermic bond energy diagram

Answer 3

The products are HIGHER than the reactants. The difference in height = the energy taken in during the reaction (per mole)
ΔT is positive here.
(From 7 to 2 on a clock, clockwise)

Question 4

What does the activation energy represent?

Answer 4

The minimum energy needed by reacting particles to break their bonds

Question 5

How does a catalyst effect activation energy on bond energy diagrams?

Answer 5

Provides a different pathway for a reaction that has a lower activation energy (so the curve is not as high)

Question 6

Activation energy is [ ] by a catalyst

Answer 6

Lowered

Question 7

When using a catalyst, what happens to the overall energy change?

Answer 7

Remains the sane = ΔT

Question 8

Calculate ΔT for H₂ + Cl₂ -> 2HCl
H–H = + 436 kJ/mol
Cl–Cl = + 242 kJ/mol
H–Cl = + 431 kJ/mol

Answer 8

Breaking bonds:
436 + 242 = 678 kJ
Forming bonds:
2 * 431 = 862 kJ
Overall more energy is released:
862 - 678 = 184 kJ/mol
Because it releases energy = exothermic
therefore for ΔT it must be negative
Final Answer = -184 kJ/mol