# 3: Chemical Reactions


Note

Sections 3.1 and 3.2 are mostly conceptional questions. These will help you prepare for the questions in sections 3.3 - 3.8.

## Identify Reactants and Products

Exercise $$\PageIndex{1}$$

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

reactants: nitrogen (N2) and hydrogen (H2)

product: ammonia (NH3)

Exercise $$\PageIndex{2}$$

From the statement “sodium metal reacts with water to produce sodium hydroxide and hydrogen,” identify the reactants and the products.

reactants: sodium (Na) and water (H2O)

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

Exercise $$\PageIndex{3}$$

From the statement “magnesium hydroxide reacts with nitric acid to produce magnesium nitrate and water,” identify the reactants and the products.

reactants: magnesium hydroxide (Mg(OH)2) and nitric acid (HNO3)

products: magnesium nitrate (Mg(NO3)2) and water (H2O)

Exercise $$\PageIndex{4}$$

From the statement “propane reacts with oxygen to produce carbon dioxide and water,” identify the reactants and the products.

reactants: propane (C3H8), oxygen (O2)

products: carbon dioxide (CO2), water (H2O)

## Conceptional Questions

Exercise $$\PageIndex{1}$$

Use the following equations to answer the next five questions:

1. $$\ce{H2O}(s)\rightarrow \ce{H2O}(l)$$
2. $$\ce{Na+}(aq)+\ce{Cl-}(aq)\ce{Ag+}(aq)+\ce{NO3-}(aq) \rightarrow \ce{AgCl}(s)+\ce{Na+}(aq)+\ce{NO3-}(aq)$$
3. $$\ce{CH3OH}(g)+\ce{O2}(g)\rightarrow \ce{CO2}(g)+\ce{H2O}(g)$$
4. $$\ce{2H2O}(l)\rightarrow \ce{2H2}(g)+\ce{O2}(g)$$
5. $$\ce{H+}(aq)+\ce{OH-}(aq)\rightarrow \ce{H2O}(l)$$

1. Which equation describes a physical change?
2. Which equation identifies the reactants and products of a combustion reaction?
3. Which equation is not balanced?
4. Which is a net ionic equation?

a.) i. $$H_2O (solid) → H_2O(liquid)$$

b.) iii.

c.) iii. $$\ce{2CH3OH}(g)+\ce{3O2}(g)\rightarrow \ce{2CO2}(g)+\ce{4H2O}(g)$$

d.) v

## Single and Double-Displacement Reactions

Exercise $$\PageIndex{2}$$

1. What are the general characteristics that help you recognize single-replacement reactions?
2. What are the general characteristics that help you recognize double-replacement reactions?
1. One element replaces another element in a compound.
2. The cations or anions of two ionic compounds are exchanged.

## Composition, Decomposition, and Combustion Reactions

Exercise $$\PageIndex{3}$$

1. Is it possible for a composition reaction to also be a combustion reaction? Give an example to support your case.
2. Is it possible for a decomposition reaction to also be a combustion reaction? Give an example to support your case.
1. Yes; 2H2 + O2 → 2H2O (answers will vary)
2.

## Identify Reaction Types

Exercise $$\PageIndex{4}$$

Identify the type equations each of the following represent:

1. 2Al2S3 + 9O2 → 2Al2O3 + 6SO2
2. 2HCl + Na2S → 2NaCl + H2S
3. 2SO2 + O2 → 2SO3
4. 3F2 + 2FeI3 → 3I2 + 2FeF3
5. 6C + 3H2 → C6H6
6. CaCO3 → CaO + CO2
7. P4 + 5O2 → 2P2O5
8. Zn + Fe(NO3)2 → Zn(NO3)2 + Fe
9. Zn(NO3)2 + 2NaOH → Zn(OH)2 + 2NaNO3
10. H2SO3 → H2O + SO2
1. Combustion
2. Double-Displacement
3. Formation, Synthesis, Combination
4. Single-Displacement
5. Formation, Synthesis, Combination
6. Decomposistion
7. Combustion
8. Single-Displacement
9. Decomposistion

## Balanced?

Exercise $$\PageIndex{1}$$

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

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.

## Balancing Equations

Exercise $$\PageIndex{3a}$$

Balance the following equations

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

PCl5(s)+H2O(l)→POCl3(l)+2HCl(aq)

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

H2(g)+I2(s)→2HI(s)

4Fe(s)+3O2(g)→2Fe2O3(s)

Exercise $$\PageIndex{3b}$$

Balance the following equations

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

2Na(s)+2H2O(l) → 2NaOH(aq)+H2(g)

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

P4(s)+6Cl2(g) → 4PCl3(l)

PtCl4(s) → Pt(s)+2Cl2(g)

Exercise $$\PageIndex{3c}$$

Balance the following equations

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

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

P4(s)+5O2(g)→P4O10(s)

2Pb(s)+2H2O(l)+O2(g)→2Pb(OH)2(s)

3Fe(s)+4H2O(l)→Fe3O4(s)+4H2(g)

Exercise $$\PageIndex{3c}$$

Balance the following equations

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

Sc2O3(s)+3SO3(l)→Sc2(SO4)3(s)

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

2Al(s)+3H2SO4(aq)→Al2(SO4)3(s)+3H2(g)

TiCl4(s)+2H2O(g)→TiO2(s)+4HCl(g)

## 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.

1. NaCl(?)
2. Pb(OH)2(?)
3. MgF2(?)
4. K2SO4(?)

NaCl(aq)

Pb(OH)2(s)

MgF2(s)

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.

1. AgCl(?)
2. PbCl2(?)
3. Ba(OH)2(?)
4. Pb3(PO4)2(?)

AgCl(s)

PbCl2(s)

Ba(OH)2(aq)

Pb3(PO4)2(s)

## Electrolytes

Exercise $$\PageIndex{4c}$$

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

1. NaCl(aq)
2. Na2SO4(aq)
3. C6H12O6(aq)  (sugar)
4. AgCl(s)

strong electrolyte, soluble salt

strong electrolyte, soluble salt

nonelectrolyte, soluble molecule

nonelectrolyte, insoluble salt

f

## Molecular, Complete Ionic and Net Ionic Equations

Exercise $$\PageIndex{1}$$

Consider molecular, complete ionic, and net ionic equations.

1. What is the difference between these types of equations?
2. In what circumstance would the complete and net ionic equations for a reaction be identical?
1. Molecular equations, or balanced equations, use molecular formulas to represent neutral ionic compounds and acids. A parentheses is used after each compound to indicate state of each substance. Net ionic equation shows only the chemical species that are involved in a reaction. Complete ionic equation shows the chemical species that are involved in a reaction and the spectator ions.
2. The complete and net ionic equations will be identical if there are no spectator ions.

## Dissociation in Water

Exercise $$\PageIndex{2}$$

Write a chemical equation that represents the following compounds dissociating in water:

1. NaBr(s)
2. (NH4)3PO4(s)
1. NaBr(s) → Na+(aq) + Br(aq)
2. (NH4)3PO4(s) → 3NH4+(aq) + PO43−(aq)

## Complete Ionic Equations

Exercise $$\PageIndex{3}$$

Write the complete ionic equation for the following reactions:

You may have to consult the solubility rules.

1. FeCl2(aq) and AgNO3(aq)
2. KCl(aq) and NaC2H3O2(aq)
1. Fe2+(aq) + 2Cl(aq) + 2Ag+(aq) + 2NO3(aq) → Fe2+(aq) + 2NO3(aq) + 2AgCl(s)

2. K+(aq) + Cl(aq) + Na+(aq) + C2H3O2(aq) → Na+(aq) + Cl(aq) + K+(aq) + C2H3O2(aq)

## Net Ionic Equations and Spectator Ions

Exercise $$\PageIndex{4}$$

Write the net ionic equation for the following reactions and if there is a net ionic equations, identify the spectator ions.

You may have to consult the solubility rules.

1. FeCl2(aq) and AgNO3(aq)
2. KCl(aq) and NaC2H3O2(aq)
1. 2Cl(aq) + 2Ag+(aq) → 2AgCl(s)

1.  Fe2+(aq) and NO3(aq)

2. There is no overall reaction. (meaning there is no precipitate formed)

## Arrhenius Acid and Base

Exercise $$\PageIndex{1}$$

1. What is the Arrhenius definition of an acid?
2. What is the Arrhenius definition of a base?
1. An Arrhenius acid increases the amount of H+ ions in an aqueous solution.
2. An Arrhenius base increases the amount of OH- ions in an aqueous solution.

## Predict Products

Exercise $$\PageIndex{2}$$

Predict the products of each acid-base combination listed. Assume that a neutralization reaction occurs.

1. HCl and KOH
2. H2SO4 and KOH
3. H3PO4 and Ni(OH)2
1. KCl and H2O
2. K2SO4 and H2O
3. Ni3(PO4)2 and H2O

## Balance Equations

Exercise $$\PageIndex{3}$$

Write a balanced chemical equation for each neutralization reaction in Exercise 3.6.2.

1. HCl + KOH → KCl + H2O
2. H2SO4 + 2KOH → K2SO4 + 2H2O
3. 2H3PO4 + 3Ni(OH)2 → Ni3(PO4)2 + 6H2O

Exercise $$\PageIndex{4}$$

Write a balanced chemical equation for the neutralization reaction between each given acid and base. Include the proper phase labels.

1. HI(aq) + KOH(aq) → ?
2. H2SO4(aq) + Ba(OH)2(aq) → ?
1. HI(aq) + KOH(aq) → KCl(aq) + H2O(ℓ)
2. H2SO4(aq) + Ba(OH)2(aq) → BaSO4(s) + 2H2O(ℓ)

## Complete and Net Ionic Equations

Exercise $$\PageIndex{5}$$

Write the complete and net ionic equations for the neutralization reaction between HClO3(aq) and Zn(OH)2(s). Assume the salt is soluble.

Complete ionic equation: 2H+(aq) + 2ClO3(aq) + Zn2+(aq) + 2OH(aq) → Zn2+(aq) + 2ClO3(aq) + 2H2O(ℓ)

Net ionic equation: 2H+(aq) + 2OH(aq) → 2H2O(ℓ)

## Definitions

Exercise $$\PageIndex{1}$$

1. What are two different definitions of oxidation?
2. What are two different definitions of reduction?
1. loss of electrons; increase in oxidation number
2. increase of electrons; decrease in oxidation nuumber

## Movement of Electrons

Exercise $$\PageIndex{1}$$

In the reaction

2Ca(s) + O2(g) → 2CaO

indicate what has lost electrons and what has gained electrons.

Ca has lost electrons, and O has gained electrons.

Exercise $$\PageIndex{2}$$

In the reaction

2Li(s) + O2(g) → Li2O2(s)

indicate what has been oxidized and what has been reduced.

Li has been oxidized, and O has been reduced.

## Oxidation Numbers

Exercise $$\PageIndex{2}$$

Assign oxidation numbers to each atom in each substance.

1. CH2O
2. NH3
3. Rb2SO4
4. Zn(C2H3O2)2
1. C: 0; H: +1; O: −2
2. N: −3; H: +1
3. Rb: +1; S: +6; O: −2
4. Zn: +2; C: 0; H: +1; O: −2

## Redox by Oxidation Numbers

Exercise $$\PageIndex{2}$$

Identify what is being oxidized and reduced in this redox equation by assigning oxidation numbers to the atoms.

2KrF2 + 2H2O → 2Kr + 4HF + O2

K is being oxidized, and Mg is being reduced.

## Balance Gas Formation Equations

Exercise $$\PageIndex{1}$$

Lithium hydroxide may be used to absorb carbon dioxide in enclosed environments, such as manned spacecraft and submarines. Write an equation for the reaction that involves 2 mol of LiOH per 1 mol of CO2. (Hint: Water is one of the products.)

$$\ce{2LiOH}(aq)+\ce{CO2}(g)\rightarrow \ce{Li2CO3}(aq)+\ce{H2O}(l)$$

Exercise $$\PageIndex{2}$$

Complete and balance the equations of the following reactions, each of which could be used to remove hydrogen sulfide from natural gas:

1. $$\ce{Ca(OH)2}(s)+\ce{H2S}(g) \rightarrow$$
2. $$\ce{Na2CO3}(aq)+\ce{H2S}(g)\rightarrow$$
1. $$\ce{Ca(OH)2}(s)+\ce{H2S}(g)\rightarrow \ce{CaS}(s)+\ce{2H2O}(l)$$;
2. $$\ce{Na2CO3}(aq)+\ce{H2S}(g)\rightarrow \ce{Na2S}(aq)+\ce{CO2}(g)+\ce{H2O}(l)$$

Exercise $$\PageIndex{3}$$

Write balanced chemical equations for the reactions used to prepare each of the following compounds from the given starting material(s). In some cases, additional reactants may be required.

1. solid ammonium nitrate from gaseous molecular nitrogen via a two-step process (first reduce the nitrogen to ammonia, then neutralize the ammonia with an appropriate acid)
2. gaseous hydrogen bromide from liquid molecular bromine via a one-step redox reaction
3. gaseous H2S from solid Zn and S via a two-step process (first a redox reaction between the starting materials, then reaction of the product with a strong acid)
1. step 1: $$\ce{N2}(g)+\ce{3H2}(g)\rightarrow \ce{2NH3}(g)$$ , step 2: $$\ce{NH3}(g)+\ce{HNO3}(aq)\rightarrow \ce{NH4NO3}(aq)\rightarrow \ce{NH4NO3}(s)\ce{(after\: drying)}$$;
2. $$\ce{H2}(g)+\ce{Br2}(l)\rightarrow \ce{2HBr}(g)$$;
3. $$\ce{Zn}(s)+\ce{S}(s)\rightarrow \ce{ZnS}(s)$$ and $$\ce{ZnS}(s)+\ce{2HCl}(aq)\rightarrow \ce{ZnCl2}(aq)+\ce{H2S}(g)$$

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