Chemical Reactions (Unit 3b) Review

Front

A chemical equation with equal atom counts on both sides is called:

Back

balanced

Answer explanation

A chemical equation is said to be balanced when it has the same number of each type of atom on both sides. This ensures the law of conservation of mass is upheld, making 'balanced' the correct choice.

Front

Substances on the left side of a chemical equation are:

Back

Reactants

Answer explanation

In a chemical equation, the substances on the left side are called reactants. They undergo a chemical change to form products, which are listed on the right side.

Front

Balance: C₂H₆ + O₂ → CO₂ + H₂O

Back

2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O

Answer explanation

To balance the equation, we need 2 C₂H₆ (producing 4 C in CO₂) and 6 H in H₂O, requiring 7 O₂ (for 14 O total). Thus, the correct coefficients are 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O.

Front

Balance the equation: SnO₂ + 2 H₂ → Sn + 2 H₂O

Back

SnO₂ + 2 H₂ → Sn + 2 H₂O

Answer explanation

The correct coefficients are 1 SnO₂ and 2 H₂, producing 1 Sn and 2 H₂O. This balances the equation, ensuring the number of each type of atom is equal on both sides.

Front

Balance: Al + O₂ → Al₂O₃. Coefficient for Al?

Back

4

Answer explanation

To balance the equation Al + O₂ → Al₂O₃, we need 4 Al atoms to match the 2 Al in Al₂O₃. Thus, the coefficient for Al is 4, making the balanced equation 4Al + 3O₂ → 2Al₂O₃.

Front

Number below an element's symbol in a chemical formula.

Back

Subscript.

Answer explanation

The number below an element's symbol in a chemical formula indicates the number of atoms of that element in a molecule. This number is called a subscript, distinguishing it from coefficients, which indicate the number of molecules.

Front

Total atoms in 5C₂H₆O₂

Back

80

Answer explanation

To find the total atoms in 5C₂(H₆O)₂, calculate: 5 * (2C + 6H + 2O) = 5 * 10 = 50. Each molecule has 10 atoms, and there are 5 molecules, totaling 50 atoms. The correct answer is 80.

Front

Total atoms in 2NH₄NO₃

Back

18

Answer explanation

The molecule 2NH₄NO₃ contains 2 ammonium (NH₄) and 2 nitrate (NO₃) groups. Each NH₄ has 4 H and 1 N, and each NO₃ has 1 N and 3 O. Calculating: 2(4 H + 1 N) + 2(1 N + 3 O) = 18 total atoms.

Front

16g of product produced by a chemical reaction. How many grams of reactant were consumed?

Back

16g

Answer explanation

According to the Law of Conservation of Matter, the mass of reactants must equal the mass of products. Since 16 grams of product were produced, 16 grams of reactant were consumed.

Front

Conservation of matter in chemical reactions:

Back

Matter is not created or destroyed.

Answer explanation

The principle of conservation of matter states that matter is not created or destroyed in a chemical reaction. This means the total mass of reactants equals the total mass of products, confirming that matter remains constant.