Question

quiz 8.6be- counting atoms, chemical equations and the law of conservation of mass
the photo shows the reaction between zinc and hydrochloric acid that forms zinc chloride and hydrogen gas.
analyze the chemical equations. which of these formulas correctly shows how matter is conserved?

• zn + 2hcl → zncl₂ + h₂
• zn + 4hcl → zncl₂ + 2h₂
• zn + 2hcl → zncl₂ + 2h₂
• zn + hcl → zncl₂ + h₂

Explanation:

To determine which equation conserves matter, we check the number of each atom on both sides (Law of Conservation of Mass).

• For the first option ($\text{Zn} + 2\text{HCl}

ightarrow \text{ZnCl}_2 + \text{H}_2$):

• Zn: 1 on left, 1 on right.
• H: $2\times1 = 2$ on left, $2\times1 = 2$ on right.
• Cl: $2\times1 = 2$ on left, 2 on right.
• Second option ($\text{Zn} + 4\text{HCl}

ightarrow \text{ZnCl}_2 + 2\text{H}_2$): Cl on left is 4, right is 2 (not conserved).

• Third option ($\text{Zn} + 2\text{HCl}

ightarrow \text{ZnCl}_2 + 2\text{H}_2$): H on left is 2, right is 4 (not conserved).

• Fourth option ($\text{Zn} + \text{HCl}

ightarrow \text{ZnCl}_2 + \text{H}_2$): Cl on left is 1, right is 2 (not conserved); H on left is 1, right is 2 (not conserved).

Only the first equation has equal numbers of each atom on both sides.

Answer:

A. $\text{Zn} + 2\text{HCl}
ightarrow \text{ZnCl}_2 + \text{H}_2$