How much do oxygen gas and hydrogen gas expand

Question

when exposed to high heat.

Answer 1

That is far too ambiguous a question.  It will depend on the original pressure, volume and temperature of the gases, and to what new temperature the gases are raised.  

The volumes are related by the combined gas law:

P1V1 / T1 = P2V2 / T2

Where P, V and T are the pressure, volume and absolute temperature of (1) the original conditions, and (2) the new conditions.

Solve for the new volume (V2) and plug in all the other numbers.

V2 = P1V1T2 / T1P2

Answer 2

Actually

on wikipedia