Question

1. choose the best answer. which of these describes the law of conservation of mass? mass$_{reactants}$ > mass$_{products}$ mass$_{reactants}$ ≈ mass$_{products}$ mass$_{reactants}$ < mass$_{products}$ mass$_{reactants}$ = mass$_{products}$

Explanation:

(for reaction classification):

Step1: Identify reaction 1 type

$2\text{NH}_3 + \text{H}_2\text{SO}_4
ightarrow (\text{NH}_4)_2\text{SO}_4$: Two reactants form one product, so it is synthesis.

Step2: Identify reaction 2 type

$4\text{C}_5\text{H}_9\text{O} + 27\text{O}_2
ightarrow 20\text{CO}_2 + 18\text{H}_2\text{O}$: A compound reacts with $\text{O}_2$ to produce $\text{CO}_2$ and $\text{H}_2\text{O}$, so it is combustion.

Step3: Identify reaction 3 type

$3\text{Pb} + 2\text{H}_3\text{PO}_4
ightarrow 3\text{H}_2 + \text{Pb}_3(\text{PO}_4)_2$: A metal replaces hydrogen in an acid, so it is single replacement.

Step4: Identify reaction 4 type

$\text{Li}_3\text{N} + 3\text{NH}_4\text{NO}_3
ightarrow 3\text{LiNO}_3 + (\text{NH}_4)_3\text{N}$: Cations/anions swap between two compounds, so it is double replacement.

Step5: Identify reaction 5 type

$2\text{Na}_2\text{O}
ightarrow 4\text{Na} + \text{O}_2$: One compound breaks into simpler substances, so it is decomposition.

(for mass law question):

Step1: Recall law of conservation of mass

The law states total mass of reactants equals total mass of products.

Answer:

Reaction Classifications:

1. $2\text{NH}_3 + \text{H}_2\text{SO}_4

ightarrow (\text{NH}_4)_2\text{SO}_4$: synthesis

1. $4\text{C}_5\text{H}_9\text{O} + 27\text{O}_2

ightarrow 20\text{CO}_2 + 18\text{H}_2\text{O}$: combustion

1. $3\text{Pb} + 2\text{H}_3\text{PO}_4

ightarrow 3\text{H}_2 + \text{Pb}_3(\text{PO}_4)_2$: single replacement

1. $\text{Li}_3\text{N} + 3\text{NH}_4\text{NO}_3

ightarrow 3\text{LiNO}_3 + (\text{NH}_4)_3\text{N}$: double replacement

1. $2\text{Na}_2\text{O}

ightarrow 4\text{Na} + \text{O}_2$: decomposition

Law of Conservation of Mass:

$\text{Mass}_{\text{reactants}} = \text{Mass}_{\text{products}}$ (the last option)