Answer:
When iron filings and sulphur powder are mixed and heated they undergo a chemical reaction and form ferrous sulphide (FeS). It is a new substance which has properties entirely different from Fe and S. Therefore, heating of mixture of iron and sulphur powder is a chemical change.
You multiply the percentage and theoretical yield together.
Answer:

Explanation:
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In this case, since the combustion of butane is:

Thus, since the molar mass of butane is 58.12 g/mol and that of carbon dioxide is 44.01 g/mol, we obtain the following mass of CO2 product:

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