Mass Changes when a Reactant or Product is a Gas (OCR GCSE Chemistry A (Gateway Science Suite)): Revision Notes
📚 Revision Notes
3.1.3 Mass Changes when a Reactant or Product is a Gas
Why Does Mass Seem to Change in Some Reactions?
Even though mass is conserved, it might seem like the mass changes if one of the reactants or products is a gas. This is because gases can escape or enter a reaction container, making it look like mass is lost or gained.
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Example 1: Apparent Loss of Mass:
- When heating calcium carbonate , it decomposes into calcium oxide (CaO) and carbon dioxide . If the reaction is done in an open container, the carbon dioxide gas can escape, making it look like the mass has decreased.
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Example 2: Apparent Gain of Mass:
- If you leave a piece of iron exposed to air, it reacts with oxygen to form iron oxide (rust). The iron appears to gain mass because oxygen from the air has combined with it.