The total mass increases. The total mass decreases. The total mass remains the same. Part of the mass is changed to heat energy.
I gave my students this multiple choice question: When a mixture of oxygen and hydrogen is ignited in a test tube, the reaction shown occurs. Hydrogen + Oxygen -> Water + Energy What happens to the total mass of the contents of the test tube?

Only one answer is correct among these 4 choices:
- The total mass increases.
- The total mass decreases.
- The total mass remains the same.
- Part of the mass is changed to heat energy.

Could you tell me which one is correct?

The total mass remains the same.