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question 20
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is melting butter a physical or chemical change?
select one:
a. physical
b. chemical
question 21
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fill in the missing information for the following reaction.
iron 30 g + sulfur blank → iron (iii) sulfide 40 g

Explanation:

Question 20

Melting butter only changes its state from solid to liquid; no new substance is formed, so it is a physical change.

Step1: Apply Law of Conservation of Mass

The total mass of reactants equals the total mass of products. Let the mass of sulfur be $m$.
$\text{Mass of Iron} + m = \text{Mass of Iron (II) sulfide}$

Step2: Solve for sulfur mass

Substitute known values and calculate $m$.
$m = 40\ \text{g} - 30\ \text{g}$

Answer:

a. Physical

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Question 21