School of Science and Mathematics

p2. Reactivity of substances at high temperature

a) Sodium will be unreactive with anything at 10 000° C, including oxygen, (which itself will have decomposed into atoms).

b) Petrol will be very reactive but only to decomposition. It won’t react with oxygen at 10 000° C.

Problem 1 Concentration

Def’n : The amount of a substance divided by the volume it occupies.

Expl’n :Usually in a solution. eg. If 0.1 mol of NaCl (i.e. 5.85 g) is dissolved in 500 mL of solution, the conc’n is 0.20 mol/L. Concentration is important because the reactivity of a substance usually depends on its concentration. Also, it is often important to know how much of a substance we have. This is easily worked out from the volume and concentration of the solution.

Or similar

Problem 2

i) SI unit for distance; metre or m, Other units; mile, inch, km, mm, dm, cm, etc.

ii) SI unit for time; second or s. Other units; minute, hour, ks, ms, etc.

Problem 3

a) acc’n = 3.375 mph/s

b) = 1.5 m.s^-2

c) » 0.15 gravities of acceleration.

Problem 4

a) F = m x a = 70 kg x 9.81 m.s^-2 = 687 newtons

b) m = F/a = 22N/9.81 m.s^-2 = 2.24 kg » 5 lb