Question

the law of conservation of mass tells us that the total number of atoms does not change in a chemical reaction and thus mass is conserved. select all of the reactions that obey the law of conservation of mass a ( 4 \text{nh}_3 + 5 \text{o}_2
ightarrow 4 \text{no} + 6 \text{h}_2\text{o} ) b ( 8 \text{h}_2\text{s} + 8 \text{cl}_2
ightarrow \text{s}_8 + 16 \text{hcl} ) c ( \text{ch}_4 + 2 \text{o}_2
ightarrow \text{co}_2 + \text{h}_2\text{o} ) d ( \text{hcl} + \text{k}_2\text{co}_3
ightarrow \text{kcl} + \text{h}_2\text{o} + \text{co}_2 ) e ( 2 \text{al(oh)}_3 + 3 \text{h}_2\text{so}_4
ightarrow \text{al}_2(\text{so}_4)_3 + 6 \text{h}_2\text{o} )

Explanation:

To determine which reactions obey the law of conservation of mass, we check the number of each type of atom on both sides of the equation (reactants and products).

Reaction A: \( 4NH_3 + 5O_2

ightarrow 4NO + 6H_2O \)

• Nitrogen (N): Left side: \( 4 \) (from \( 4NH_3 \)); Right side: \( 4 \) (from \( 4NO \)). Balanced.
• Hydrogen (H): Left side: \( 4 \times 3 = 12 \) (from \( 4NH_3 \)); Right side: \( 6 \times 2 = 12 \) (from \( 6H_2O \)). Balanced.
• Oxygen (O): Left side: \( 5 \times 2 = 10 \) (from \( 5O_2 \)); Right side: \( 4 \times 1 + 6 \times 1 = 10 \) (from \( 4NO \) and \( 6H_2O \)). Balanced.

This reaction obeys the law.

Reaction B: \( 8H_2S + 8Cl_2

ightarrow S_8 + 16HCl \)

• Hydrogen (H): Left side: \( 8 \times 2 = 16 \) (from \( 8H_2S \)); Right side: \( 16 \times 1 = 16 \) (from \( 16HCl \)). Balanced.
• Sulfur (S): Left side: \( 8 \times 1 = 8 \) (from \( 8H_2S \)); Right side: \( 8 \) (from \( S_8 \)). Balanced.
• Chlorine (Cl): Left side: \( 8 \times 2 = 16 \) (from \( 8Cl_2 \)); Right side: \( 16 \times 1 = 16 \) (from \( 16HCl \)). Balanced.

This reaction obeys the law.

Reaction C: \( CH_4 + 2O_2

ightarrow CO_2 + H_2O \)

• Carbon (C): Left side: \( 1 \) (from \( CH_4 \)); Right side: \( 1 \) (from \( CO_2 \)). Balanced.
• Hydrogen (H): Left side: \( 4 \) (from \( CH_4 \)); Right side: \( 2 \) (from \( H_2O \)). Not balanced (needs \( 2H_2O \) to balance H).

This reaction does not obey the law.

Reaction D: \( HCl + K_2CO_3

ightarrow KCl + H_2O + CO_2 \)

• Potassium (K): Left side: \( 2 \) (from \( K_2CO_3 \)); Right side: \( 1 \) (from \( KCl \)). Not balanced (needs \( 2KCl \) to balance K).

This reaction does not obey the law.

Reaction E: \( 2Al(OH)_3 + 3H_2SO_4

ightarrow Al_2(SO_4)_3 + 6H_2O \)

• Aluminum (Al): Left side: \( 2 \) (from \( 2Al(OH)_3 \)); Right side: \( 2 \) (from \( Al_2(SO_4)_3 \)). Balanced.
• Sulfur (S): Left side: \( 3 \times 1 = 3 \) (from \( 3H_2SO_4 \)); Right side: \( 3 \) (from \( Al_2(SO_4)_3 \)). Balanced.
• Oxygen (O): Left side: \( 2 \times 3 + 3 \times 4 = 6 + 12 = 18 \); Right side: \( 3 \times 4 + 6 \times 1 = 12 + 6 = 18 \). Balanced.
• Hydrogen (H): Left side: \( 2 \times 3 + 3 \times 2 = 6 + 6 = 12 \); Right side: \( 6 \times 2 = 12 \). Balanced.

This reaction obeys the law.

Answer:

A. \( 4NH_3 + 5O_2
ightarrow 4NO + 6H_2O \)
B. \( 8H_2S + 8Cl_2
ightarrow S_8 + 16HCl \)
E. \( 2Al(OH)_3 + 3H_2SO_4
ightarrow Al_2(SO_4)_3 + 6H_2O \)