Conservation in Chemical Reactions Quick Check. 1 correct answer per question.

Question

1. In which chemical equation is the number of atoms in the reactants the same as the number of atoms in the products?
a. CH4 + O2 → CO2 + 2H2O
b. Li2CO3 → LiO + CO2
c. CO2 + H2O → CH2OH + O2
d. Zn + 2HCl → H2 + ZnCl2

2. Which statement is true regarding a chemical reaction?
a. Even if the total number of atoms does not change, mass may not be conserved in the reaction.
b. The total number of atoms changes, so mass is conserved in the reaction.
c. The total number of atoms does not change, so mass is conserved in the reaction.
d. Even if the total number of atoms changes, mass may not be conserved in the reaction.

3. Use the equation and the table to answer the question.

FeCl3 + 3H2O → Fe(OH)3 + 3HCl

Element Mass of an Atom (amu)
Fe 56
Cl 35
H 1
O 16
Iron chloride and water react according to the equation shown. The table shows the atomic masses of the elements involved in the reaction. What is the total mass of the reactants?
a. 161 amu
b. 179 amu
c. 215 amu
d. 108 amu

4. In a chemical reaction, two molecules with a total mass of 76 amu react to form a single molecule. What is the mass of the molecule that is formed?
a. 228 amu
b. 76 amu
c. 152 amu
d. 38 amu

Answer 1

Here are the correct answers to the conservation in chemical reactions quick check:

1. a. CH4 + O2 → CO2 + 2H2O

   • This equation has the same number of atoms on both sides: 1 carbon, 4 hydrogens, and 4 oxygens.

2. c. The total number of atoms does not change, so mass is conserved in the reaction.

   • According to the law of conservation of mass, the total mass and number of atoms remain constant in a chemical reaction.

3. c. 215 amu

   • Calculate total mass of the reactants:
     • FeCl3: 1(56) + 3(35) = 56 + 105 = 161 amu
     • 3H2O: 3(2) + 3(16) = 6 + 48 = 54 amu
     • Total mass of reactants = 161 + 54 = 215 amu.

4. b. 76 amu

   • The mass of the formed molecule must equal the mass of the reactants according to the law of conservation of mass.

Final answers:

1. a
2. c
3. c
4. b