Question

1. choose the best answer.

when the following equation is balanced, what is the coefficient for o₂?
——c₃h₈ + ——o₂ → ——co₂ + ——h₂o
options: 6, 2, 5, 3

1. choose the best answer.

for their lab report, students must describe a chemical reaction in words.
which of the following would represent the correct word equation for this equation?
cu (s) + agno₃ (aq) → cu(no₃)₂ (aq) + ag (s)
options:
solid copper and silver nitrate, dissolved in water, react to form aqueous copper (ii) nitrate and solid silver.
solid copper and silver (iii) nitrogen oxide, dissolved in water, react to form aqueous copper (ii) nitrate and solid silver.
solid copper and silver nitrite, dissolved in water, react to form aqueous zinc nitrite and solid silver.
solid copper and silver nitrate, dissolved in water, react to form aqueous copper nitrate and solid silver.

Explanation:

Step1: Balance C atoms

Start with the unbalanced equation: $\ce{C3H8 + O2 -> CO2 + H2O}$.
There are 3 C on left, so set $\ce{CO2}$ coefficient to 3:
$\ce{C3H8 + O2 -> 3CO2 + H2O}$

Step2: Balance H atoms

There are 8 H on left, so set $\ce{H2O}$ coefficient to 4 (since $4\times2=8$):
$\ce{C3H8 + O2 -> 3CO2 + 4H2O}$

Step3: Balance O atoms

Count O on right: $3\times2 + 4\times1 = 10$. So set $\ce{O2}$ coefficient to 5 (since $5\times2=10$):
$\ce{C3H8 + 5O2 -> 3CO2 + 4H2O}$

Step4: Verify word equation match

Match the chemical equation $\ce{Cu(s) + AgNO3(aq) -> Cu(NO3)2(aq) + Ag(s)}$ to word descriptions:

• Reactants: Solid copper, aqueous silver nitrate (dissolved in water)
• Products: Aqueous copper(II) nitrate, solid silver

Answer:

1. 5
2. Solid copper and silver nitrate, dissolved in water, react to form aqueous copper (II) nitrate and solid silver.