Question

Water (H2O) is a compound required for survival by living organisms. The diagram below shows the chemical reaction of hydrogen gas (H2) with oxygen gas (O2) to form water (H2O).



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The following question has two parts. First, answer Part A. Then, answer Part B.



Part A:

In the chemical reaction forming water, the total mass of the hydrogen molecules in the reactants is 5 grams and the total mass of the oxygen molecule in the reactants is 40 grams. What is the total mass of the water molecules produced?


10 grams


20 grams


35 grams


45 grams



Part B:

Which statement BEST supports the choice from Part A?


The total mass of the reactants is half the total mass of the products.


The total mass of the reactants is double the total mass of the products.


The total mass of the reactants is equal to the total mass of the products.


The total mass of the reactants is equal to one of the compounds in the products.

Answer 1

Part A: 45 grams.

Part B: The total mass of the reactants is equal to the total mass of the products.

Explanation: By conservation of mass, mass is neither created nor destroyed in a chemical reaction, so 5 g H2 + 40 g O2 = 45 g H2O.