5: Chemical Reactions

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Introduction to Chemical Reactions

Exercise \(\PageIndex{1a}\)

From the statement “nitrogen and hydrogen react to produce ammonia,” identify the reactants and the products.

Answer

reactants: nitrogen (N₂) and hydrogen (H₂)

product: ammonia (NH₃)

Exercise \(\PageIndex{1b}\)

From the statement “sodium hydroxide and water are produced when sodium metal reacts with water” identify the reactants and the products.

Answer

reactants: sodium (Na) and water (H₂O)

products: sodium hydroxide (NaOH) and hydrogen (H₂)

Exercise \(\PageIndex{1c}\)

What does it mean to say an equation is balanced? Why is it important for an equation to be balanced?

Answer: An equation is balanced when the same number of each element is represented on the reactant and product sides. Equations must be balanced to accurately reflect the law of conservation of matter.

Types of Chemical Reactions

Exercise \(\PageIndex{2a}\)

Identify the type of reaction

2C₂H₆ + 7O₂ → 4CO₂+ 6H₃O
2HCl + Na₂S → 2NaCl + H₂S
2SO₂ + O₂ → 2SO₃
Zn + Fe(NO₃)₂ → Zn(NO₃)₂ + Fe

Answer a: combustion

Answer b: double displacement

Answer c: formation (synthesis)

Answer d: Single displacement

Balancing Chemical Equations

Exercise \(\PageIndex{3a}\)

Balance the following equations

PCl₅(s)+H₂O(l) → POCl₃(l)+HCl(aq)
Cu(s)+HNO₃(aq) → Cu(NO₃)₂(aq)+H₂O(l)+NO(g)
H₂(g)+I₂(s) → HI(s)
Fe(s)+O₂(g) → Fe₂O₃(s)

Answer a: PCl₅(s)+H₂O(l)→POCl₃(l)+2HCl(aq)

Answer b: 3Cu(s)+8HNO₃(aq)→3Cu(NO₃)₂(aq)+4H₂O(l)+2NO(g)

Answer c: H₂(g)+I₂(s)→2HI(s)

Answer d: 4Fe(s)+3O₂(g)→2Fe₂O₃(s)

Exercise \(\PageIndex{3b}\)

Balance the following equations

Na(s)+H₂O(l) → NaOH(aq)+H₂(g)
(NH₄)₂Cr₂O₇(s) → Cr₂O₃(s)+N₂(g)+H₂O(g)
P₄(s)+Cl₂(g) → PCl₃(l)
PtCl₄(s) → Pt(s)+Cl₂(g)

Answer a: 2Na(s)+2H₂O(l) → 2NaOH(aq)+H₂(g)

Answer b: (NH₄)₂Cr₅₂O₇(s) → Cr₂O₃(s)+N₂(g)+4H₂O(g)

Answer c: P₄(s)+6Cl₂(g) → 4PCl₃(l)

Answer d: PtCl₄(s) → Pt(s)+2Cl₂(g)

Exercise \(\PageIndex{3c}\)

Balance the following equations

Ag(s)+H₂S(g)+O2(g) → Ag₂S(s)+H₂O(l)
P₄(s)+O₂(g)→P₄O₁₀(s)
Pb(s)+H₂O(l)+O₂(g)→Pb(OH)₂(s)
Fe(s)+H₂O(l)→Fe₃O₄(s)+H₂(g)

Answer a: 4Ag(s)+2H₂S(g)+O₂(g) → 2Ag₂S(s)+2H₂O(l)

Answer b: P₄(s)+5O₂(g)→P₄O₁₀(s)

Answer c: 2Pb(s)+2H₂O(l)+O₂(g)→2Pb(OH)₂(s)

Answer d: 3Fe(s)+4H₂O(l)→Fe₃O₄(s)+4H₂(g)

Exercise \(\PageIndex{3c}\)

Balance the following equations

Sc₂O₃(s)+SO₃(l)→Sc₂(SO₄)₃(s)
Ca₃(PO₄)₂(aq)+H₃PO₄(aq)→Ca(H₂PO₄)₂(aq)
Al(s)+H₂SO₄(aq)→Al₂(SO₄)₃(s)+H₂(g)
TiCl₄(s)+H₂O(g)→TiO₂(s)+HCl(g)

Answer a: Sc₂O₃(s)+3SO₃(l)→Sc₂(SO₄)₃(s)

Answer b: Ca₃(PO₄)₂(aq)+4H₃PO₄(aq)→3Ca(H₂PO₄)₂(aq)

Answer c: 2Al(s)+3H₂SO₄(aq)→Al₂(SO₄)₃(s)+3H₂(g)

Answer d: TiCl₄(s)+2H₂O(g)→TiO₂(s)+4HCl(g)

Aqueous Reactions

Solubility Rules

Exercise \(\PageIndex{4a}\)

Use the solubility rules to determine if the following compounds are soluble or insoluble. Indicate answer by writing formula followed by (aq) for soluble and (s) for insoluble.

NaCl(?)
Pb(OH)₂(?)
MgF₂(?)
K₂SO₄(?)

Answer a: NaCl(aq)

Answer b: Pb(OH)₂(s)

Answer c: MgF₂(s)

Answer d: K₂SO₄(aq)

Exercise \(\PageIndex{4b}\)

Use the solubility rules to determine if the following compounds are soluble or insoluble. Indicate answer by writing formula followed by (aq) for soluble and (s) for insoluble.

AgCl(?)
PbCl₂(?)
Ba(OH)₂(?)
Pb₃(PO₄)₂(?)

Answer a: AgCl(s)

Answer b: PbCl₂(s)

Answer c: Ba(OH)₂(aq)

Answer d: Pb₃(PO₄)₂(s)

Exercise \(\PageIndex{4c}\)

Identify the following as a strong electrolyte, a weak electrolyte, or a non-electrolyte, and why

NaCl(aq)
Na₂SO₄(aq)
C₆H₁₂O₆(aq) (sugar)
AgCl(s)

Answer a: strong electrolyte, soluble salt

Answer b: strong electrolyte, soluble salt

Answer c: nonelectrolyte, soluble molecule

Answer d: nonelectrolyte, insoluble salt

Predicting Products and Balancing Eqs

Exercise \(\PageIndex{4d}\)

Predict products and balance the equation

Al(NO₃)₃(aq) + Na₂(CO₃)(aq)
Pb(ClO₄)₂(aq) + Na₂SO₄(aq)
(NH₄)₃PO₄(aq) + NaOH(aq)
(NH₄)₃PO₃(aq) + CaSO₄(aq)

Answer a: 2 Al(NO₃)₃(aq) + 3 Na₂(CO₃)(aq)-> Al₂(CO₃)₃(s) + 6 NaNO₃(aq)

Answer b: Pb(ClO₄)₂(aq) + Na₂SO₄(aq) -> PbSO₄(s) + 2 NaClO₄(aq)

Answer c: (NH₄)₃PO₄(aq) + 3 NaOH(aq) -> 3NH₄OH(aq) + Na₃PO₄(aq)

Answer d: 2(NH₄)₃PO₄(aq) + 3 CaSO₄(aq) -> 3(NH₄)₂SO₄(aq) + Ca₃(PO₄)₂(S)

Exercise \(\PageIndex{4e}\)

Predict products and balance the equation

(NH₄)₂SO₄(aq) + CaCl₂(aq)
AgCH₃CO₂ (aq) + KCl(aq)
Pb(NO₃)₂(aq) + Na₂SO₄(aq)
NaOH + CaCl₂(aq)

Answer a: (NH₄)₂SO₄(aq) + CaCl₂(aq) -> CaSO₄(s) + 2 NH₄Cl(aq)

Answer b: AgCH₃CO₂ (aq) + KCl(aq) -> AgCl(s) + KCH₃CO₂(aq)

Answer c: Pb(NO₃)₂(aq) + Na₂SO₄(aq) -> PbSO₄(s)+ 2 NaNO₃(aq)

Answer d: 2 NaOH + CaCl₂(aq) -> 2 NaCl(aq) + Ca(OH)₂

Exercise \(\PageIndex{4f}\)

Predict products and balance the equation

BaI₂(aq) + H₂SO₄(aq)
Mg(s) + FeCl₃(aq)
AgNO₃(aq) + Ca(s)
Na(s) + HCl(aq)
Na(s) + H₂O(l)

Answer a: BaI₂ + H₂SO₄(aq) -> 2 HI(aq) + BaSO₄(s)

Answer b: 3 Mg(s) + 2 FeCl₃(aq)-> 2 Fe(s) + 3 MgCl₂(aq)

Answer c: 2 AgNO₃(aq) + Ca(s)-> 2 Ag(s) + Ca(NO₃)₂(aq)

Answer d: 2 Na(s) + 2 HCl(aq) -> H₂(g) + 2 NaCl(aq)
Answer e: 2 Na(s) + 2 H₂O(l) -> H₂(g) + 2 NaOH(aq)

Net, Total and General Ionic Eqs

Exercise \(\PageIndex{4g}\)

Predict products, write general, total ionic and net ionic equations (this is problem 5.4d above)

Al(NO₃)₃(aq) + Na₂(CO₃)(aq)
Pb(ClO₄)₂(aq) + Na₂SO₄(aq)
(NH₄)₃PO₄(aq) + NaOH(aq)
(NH₄)₃PO₃(aq) + CaSO₄(aq)

Answer a

2 Al(NO₃)₃(aq) + 3 Na₂(CO₃)(aq)-> Al₂(CO₃)₃(s) + 6 NaNO₃(aq) (general)

2Al⁺³(aq) +6NO₃^-(aq) + 6Na⁺(aq)+3CO₃^-2(aq)-> Al₂(CO₃)₃(s) + 6Na⁺(aq)+ 6NO₃^-(aq) (total ionic)

2Al⁺³(aq) +3CO₃^-2(aq)-> Al₂(CO₃)₃(s) (net ionic)

Answer b

Pb(ClO₄)₂(aq) + Na₂SO₄(aq) -> PbSO₄(s) + 2 NaClO₄(aq) (general)

Pb⁺²(aq) +2ClO₄^-(aq) + 2Na⁺(aq) + SO₄^-2(aq) -> PbSO₄(s) + 2Na⁺(aq) + 2ClO₄^-(aq) (total ionic)

Pb⁺²(aq) + SO₄^-2(aq) -> PbSO₄(s) (net ionic)

Answer c

(NH₄)₃PO₄(aq) + 3 NaOH(aq) -> 3NH₄OH(aq) + Na₃PO₄(aq) (general)

3NH₄⁺(aq)+ PO₄^-3(aq) + 3Na⁺(aq) + 3OH^-(aq) -> 3NH₄⁺(aq)+ PO₄^-3(aq) + 3Na⁺(aq) + 3OH^-(aq) (total ionic)

no reaction (net ionic)

Answer d

2(NH₄)₃PO₄(aq) + 3 CaSO₄(aq) -> 3(NH₄)₂SO₄(aq) + Ca₃(PO₄)₂(S) (general)

6NH₄⁺(aq)+ PO₄^-3(aq) + 3Ca⁺²(aq) + SO₄^-2(aq) -> 6NH₄⁺(aq)+ 3SO₄^-2(aq) + Ca₃(PO₄)₂(S) (total ionic)

PO₄^-3(aq) + 3Ca⁺²(aq) -> Ca₃(PO₄)₂(S) (total ionic)

Neutralization Reactions

Exercise \(\PageIndex{5a}\)

Answer the following

What is the Arrhenius definition of an acid?
What is the Arrhenius definition of an base?
What is the Bronsted definition of an acid?
What is the Bronsted definition of an base?

Answer a: Substance which increases hydronium ion concentration in water

Answer b: substance that increases hydroxide concentration in water

Answer c: Proton donor

Answer d: proton acceptor

Exercise \(\PageIndex{4g}\)

Predict products, write general, total ionic and net ionic equations

HNO₃(aq) + NaOH(aq)
Ba(OH)₂(aq) + H₂SO₄(aq)
HC₂H₃O₂(aq) + NaOH(aq)
H₃PO₃(aq) + Ca(OH)₂(aq)

Answer a

HNO₃(aq) + NaOH(aq)-> NaNO₃(aq) + H₂O(l) (general)

H⁺(aq) +NO₃^-(aq) + Na⁺(aq)+OH^-(aq)-> H₂O(l) +NO₃^-(aq) + Na⁺(aq) (total ionic)

H⁺(aq) +OH^-(aq)-> H₂O(l) (net ionic)

Answer b

Ba(OH)₂(aq) + H₂SO₄(aq) -> BaSO₄(s) + 2H₂O(l) (general)

Ba⁺²(aq) +2OH^-(aq) + 2H⁺(aq) + SO₄^-2(aq) -> BaSO₄(s) + 2H₂O(l) (total ionic)

Ba⁺²(aq) +2OH^-(aq) + 2H⁺(aq) + SO₄^-2(aq) -> BaSO₄(s) + 2H₂O(l) (net ionic)

Answer c

HC₂H₃O₂(aq) + NaOH(aq) -> NaC₂H₃O₂(aq) + H₂O(l) (general)

HC₂H₃O₂(aq) + Na⁺(aq)+ OH^-(aq) -> Na⁺(aq) + C₂H₃O₂^-(aq) + H₂O(l) (total ionic)

HC₂H₃O₂(aq) + OH^-(aq) -> C₂H₃O₂^-(aq) + H₂O(l) (net ionic)

Answer d

H₃PO₄(aq) + 3NH₄OH(aq) -> (NH₄)₃PO₄(aq) + 3H₂O(l) (general)

H₃PO₄(aq) + 3NH₄⁺(aq) + 3OH^-(aq) -> 3NH₄⁺(aq) +PO₄^-3(aq) + 3H₂O(l) (total ionic)

H₃PO₄(aq) + 3OH^-(aq) -> PO₄^-3(aq) + 3H₂O(l) (total ionic)

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