7.5 CHAPTER 7. ENERGYCHANGES IN CHEMICAL REACTIONS
In the reaction above, glucose (a type of carbohydrate in the food we eat)reacts with oxygen
from the air that we breathe in, to form carbondioxide (which we breathe out), water and
energy. The energy that is produced allows thecell to carry out its functions efficiently.
Can you see now why you are always told thatyou must eat food to get energy? It is not
the food itself that provides you with energy, but the exothermic reaction that takes place
when compounds within the food react with theoxygen you have breathed in!Exercise 7 - 1
- In each of the following reactions, say whether the reaction is endothermic or exothermic, and
give a reason for your answer.
(a) H 2 + I 2 → 2 HI + 21 kJ· mol−^1
(b) CH 4 + 2O 2 → CO 2 + 2H 2 O ΔH =− 802 kJ· mol−^1
(c) The following reaction takes place in a flask:
Ba(OH) 2. 8 H 2 O + 2NH 4 NO 3 → Ba(NO 3 ) 2 + 2NH 3 + 10H 2 O
Within a few minutes, the temperature of the flask drops by approximately 20 ◦C.
(d) 2 Na + Cl 2 → 2 NaCl ΔH =− 411 kJ· mol−^1
(e) C + O 2 → CO 2- For each of the following descriptions, say whether the process is endothermic or exothermic
and give a reason for your answer.
(a) evaporation
(b) the combustion reaction in a car engine
(c) bomb explosions
(d) melting ice
(e) digestion of food
(f) condensationMore practice video solutions or help at http://www.everythingscience.co.za(1.) 00zc (2.) 00zd7.5 Spontaneous and non-spontaneous reactions
ESBBS
Activity: Spontaneous and non-spontaneous reactions
Apparatus and materials:
A length of magnesiumribbon, thick copper wire and a Bunsen burner.