Separate: Chemistry and Extended Only
The following are two examples of substitution reactions. Only the reaction involving chlorine is a photochemical reaction.
CH4 + Cl2 → CH3Cl + HCl
CH4 + Br2 → CH3Br + HBr
i) Explain the phrase substitution reaction.
[1]
ii) How do photochemical reactions differ from other reactions?
[1]
Extended Only
Bond forming is exothermic, bond breaking is endothermic.
Explain the difference between an exothermic reaction and an endothermic reaction.
Separate: Chemistry and Extended Only
Use the bond energies to show that the following reaction is exothermic.
Bond energy is the amount of energy (kJ / mol) which must be supplied to break one mole of the bond.
Bond energies in kJ /mol | |
Cl–Cl | +242 |
C–Cl | +338 |
C–H | +412 |
H–Cl | +431 |
bonds broken energy in kJ /mol
...................... .............................
...................... .............................
total energy = .............................
bonds formed energy in kJ /mol
...................... .............................
...................... .............................
total energy = .............................
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