BMST - Basic Math and Science Chemical Reactions and Stoichiometry Questions and Answers 2 — Questions and Answers

Question 1: In a balanced chemical equation, what is conserved?

Mass and the number of atoms of each element (Correct answer)
Only the number of molecules
The volume of reactants
The temperature of the system

Correct answer: Mass and the number of atoms of each element

The law of conservation of mass requires that atoms are neither created nor destroyed in a chemical reaction.

According to the law of conservation of mass, matter cannot be created or destroyed in a chemical reaction. This means the total mass and the number of atoms of each element must be the same on both sides of a balanced equation. Balancing equations ensures this conservation by adjusting coefficients (not subscripts) so atoms are equal on both sides.

Question 2: What is the molar mass of water (H₂O)?

18 g/mol (Correct answer)
16 g/mol
20 g/mol
36 g/mol

Correct answer: 18 g/mol

H₂O = 2(1.008) + 16.00 = approximately 18 g/mol.

Molar mass is calculated by adding the atomic masses of all atoms in the molecular formula. For H₂O: 2 hydrogen atoms × 1.008 g/mol = 2.016 g/mol, plus 1 oxygen atom × 16.00 g/mol = 16.00 g/mol. Total: 2.016 + 16.00 = 18.016 g/mol, rounded to 18 g/mol.

Question 3: What type of reaction is: 2H₂ + O₂ → 2H₂O?

Synthesis (combination) (Correct answer)
Decomposition
Single replacement
Double replacement

Correct answer: Synthesis (combination)

Two or more reactants combine to form a single product, which defines a synthesis reaction.

A synthesis (combination) reaction has the general form A + B → AB, where two or more simpler substances combine to form a more complex product. In 2H₂ + O₂ → 2H₂O, hydrogen and oxygen gases combine to form water. This is distinguished from decomposition (one reactant breaks into multiple products), single replacement, and double replacement reactions.

Question 4: How many moles are in 44 grams of CO₂?

1 mole (Correct answer)
2 moles
0.5 moles
44 moles

Correct answer: 1 mole

Molar mass of CO₂ = 12 + 2(16) = 44 g/mol. So 44g ÷ 44g/mol = 1 mole.

To convert grams to moles, divide the mass by the molar mass. First, calculate the molar mass of CO₂: C = 12.01 g/mol + 2 × O = 2 × 16.00 = 32.00 g/mol, giving a total of 44.01 g/mol. Then: 44 g ÷ 44.01 g/mol ≈ 1.00 mole. This is a fundamental stoichiometric conversion.

Question 5: What is a catalyst?

A substance that speeds up a reaction without being consumed (Correct answer)
A reactant that is always used up
A product of every chemical reaction
A type of element on the periodic table

Correct answer: A substance that speeds up a reaction without being consumed

Catalysts lower the activation energy of a reaction, increasing its rate without being permanently changed.

A catalyst is a substance that increases the rate of a chemical reaction by lowering the activation energy without being consumed in the process. Catalysts provide an alternative reaction pathway with a lower energy barrier. Enzymes are biological catalysts. Catalysts do not change the equilibrium position of a reaction or the amount of product formed — they only make the reaction happen faster.

Question 6: In the reaction Fe + CuSO₄ → FeSO₄ + Cu, what type of reaction is this?

Single replacement (Correct answer)
Double replacement
Synthesis
Decomposition

Correct answer: Single replacement

Iron replaces copper in the compound because iron is more reactive than copper.

In a single replacement (single displacement) reaction, one element replaces another element in a compound. The general form is A + BC → AC + B. Here, iron (Fe) is more reactive than copper (Cu) in the activity series, so iron displaces copper from copper sulfate. The iron goes into solution as FeSO₄ while copper metal precipitates out.

BMST - Basic Math and Science Chemical Reactions and Stoichiometry Questions and Answers 2

In a balanced chemical equation, what is conserved?