Chemical Reactions

Chemical Reactions

A chemical reaction is a reaction during which substances change into one or more new substances with different physical and chemical properties. There are four types of chemical reactions:

1.  Synthesis Reactions

2.  Decomposition Reactions

3.  Single Displacement Reactions

4.  Double Displacement Reactions

Synthesis Reactions: the combination of two or more simple substances to form a more complex substance; also known as combination or addition reactions.

Shown as: A + B → AB

Example: H2(g) + O2(g) → H2O(g)

Balanced: 2H2(g) + O2(g) → 2H2O(g)

Combustion Reactions are a type of synthesis reactions. Combustion occurs if oxygen rapidly reactions with another element, forming a more complex compound by burning.

Example: S(s) + O2(g) → SO2(g)

Decomposition Reactions: the breakdown of large, more complex molecules or ionic compounds into smaller and simpler entities.

Shown as: AB → A + B

Example: H2O2(l) → O2(g) + H2O(l)

Balanced: 2H2O2(l) → O2(g) + 2H2O(l)

Single Displacement Reactions: reaction of an element and a compound to produce a new compound.

Shown as: AB + C → AC + B

Example: Zn(s) + Pb(NO3)2(aq) → Zn(NO3)2(aq) + Pb(s) (already balanced)

Double Displacement: a chemical reaction in which two compounds in aqueous solution react to form two new compounds.

Shown as: AB + CD → AD + CB

Exampl e: AgNO3(aq) + CaCl2(aq) → AgCl(s) + Ca(NO3)2(aq)

Balanced: 2AgNO3(aq) + CaCl2(aq) → 2AgCl(s) + Ca(NO3)2(aq)

In this reaction, a precipitate formed. A precipitate is a solid that forms as a result of a chemical reaction between two aqueous solutions.

Neutralization Reactions are a type of double displacement reaction in which an acid and a base react to form a salt and water.

Example: HNO3(aq) + NaOH(aq) → H2O(l) + NaNO3(s) (already balanced)

*Complete the Types of Reactions worksheet*

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Solubility and Precipitation

(with Single and Double Displacement Reactions)

Single Displacement Reactions – The Activity Series

Single displacement reactions do not always occur. Often in lab situations (and the worksheet problems we have covered), reactions are conveniently constructed so that they will occur. This is not always the case. There is a set of guidelines that will allow us to predict whether or not a single displacement reaction will proceed. If a single displacement reaction will not proceed the term ‘ NO REACTION’ or “NR” is written on the product side. This indicates that the reactants will stay as reactants and no change will occur.

The activity series (Table 4.2, attached) shows metal solids that are very reactive such as lithium and potassium at the top of the table. This indicates that they will act to displace less reactive metals from aqueous compounds that are lower on the table. The displaced metal is left on its own as a solid.

Examples: Li (s) + NaCl (aq) à LiCl (aq) + Na (s)

SnCO3 (aq) + Mg (s) à MgCO3 (aq) + Sn (s)

If, however, the lone metal is lower on the table, it is not reactive enough to displace the metal from the compound. This makes jewellery metals useful since they will not react and will remain as metals for thousands of year. In this case ‘NR’ is written.

Examples: Au (s) + HCl (aq) à NR (gold won’t decay in acid)

Cu (s) + Li(OH) (aq) à NR (pennies won’t decay in base)

Double Displacement Reactions – The Solubility Chart

Double displacement reactions are always assumed to occur. The problem is determining what type of precipitate forms. A precipitate is a new solid that appears when two aqueous solutions are mixed.

To determine the identity of the precipitate you must use the solubility table above (or Table 9.1, attached). On the solubility table, it is necessary to find one of the ions present in the possible products. If this ion is soluble, it will form an aqueous state; if the ion is insoluble, it will form a solid precipitate. This can easily be seen with a series of examples:

1. HNO3 (aq) + LiCl (aq) à HCl (aq) + Li(NO3) (aq) both H and NO3 are always soluble

2. (NH4)Cl (aq) + Ag (CH3COO) (aq) à (NH4)(CH3COO) (aq) + AgCl (s)

ammonium and acetate are soluble, but silver ions are not – they will form a solid

3. Cu2SO4 (aq) + CaCl2 (aq) à CuCl (s) + CaSO4 (s)

Cu+1 isn’t soluble with chloride ions AND calcium isn’t soluble with sulfate ions

*Complete the Reactivity Series and Solubility worksheet*

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Formula, Total & Net Ionic Equations

FORMULA UNIT EQUATION

This is the type of equation we have been dealing with previously. Basically, it is a displacement reaction.

Step 1: If no products are given, then determine the products.

Step 2: Balance the equation.

Given: lead (II) hydroxide + hydrochloric acid à

Step 1: Pb(OH)2 + HCl à PbCl2 + H2O

Step 2: Pb(OH)2 + 2 HCl à PbCl2 + 2 H2O

TOTAL IONIC EQUATION

As the name states, this equation shows ions (charges) for everything that is soluble or ionizes/dissociates 100%.

Step 3: Look at each compound in the formula unit and ask yourself: Is it soluble?

If yes, assign charges to each element in the compound

If no, then leave the compound as it is

Step 3: Pb(OH)2(s) + 2H+1 (aq) + 2 Cl-1 (aq) à Pb+2 (aq) + 2 Cl-1 (aq) + 2 H2O (l)

Question: Where did the coefficient 2 come from in front of H+1 and Cl-1?

Coefficient is the number we use to balance equations in the Formula Unit Equation. In the Total Ionic Equation, the coefficients come from:

1.  The coefficients in the formula unit equation, and

2.  From the subscript assigned when creating a compound.

If you have both a coefficient and a subscript to account for on the same compound, you would multiply the two together:

For example: Formula Unit Equation: 2 CaBr2

Total Ionic Equation: 2 Ca+2 + 4 Br-1

Spectator ions do not change their charge (remember ions are charged particles, not compounds). Whatever the charge was on the reactant side it will be the same charge on the product side of the equation. Spectators are present in the solution, but do not participate in the reaction. That is why they have no change in charge. Think of it like a sports fan: if you are a spectator, you are involved in the overall event because you are physically present and viewing the sport, but you do not participate in the action of the sport.

NET IONIC EQUATION

The Total Ionic Equation listed all the ions present. However, not all ions in the solution participate in the reaction. Ions that don`t participate in the reaction are referred to as spectator ions. These ions can be compared to spectators (the crowd) at a sporting event – the crowd is physically present and viewing the sport, but they are not involved in the action on the field. The Net Ionic Equation only accounts for the ions that participated in the chemical reaction.

Step 4: Look at each ion (not compound) in the Total Ionic Equation. Cancel out the identical spectator ions that are on both the reactant and product side.

Step 5: What remains (doesn’t cancel) constitutes the Net Ionic Equation. You will always have something that doesn’t cancel. If everything cancels, go back and check your work, something is wrong.

Step 4: Pb(OH)2 + 2H+1 + 2 Cl-1 à Pb+2 + 2 Cl-1 + 2 H2O

Step 5: Pb(OH)2 (s) + 2H+1 (aq) à Pb+2 (aq) + 2 H2O (l)

*Complete the Formula, Total Ionic, and net Ionic Equations – Practice Problems*

Types of Reactions

Balance the following equations and indicate the type of reaction taking place:

1) ____ NaBr + ____ H3PO4 à ____ Na3PO4 + ____ HBr

Type of reaction: ______

2) ____ Ca(OH)2 + ____ Al2(SO4)3 à ____ CaSO4 + ____ Al(OH)3

Type of reaction: ______

3) ____ Mg + ____ Fe2O3 à ____ Fe + ____ MgO

Type of reaction: ______

4) ____ C2H4 + ____ O2 à ____ CO2 + ____ H2O

Type of reaction: ______

5) ____ PbSO4 à ____ PbSO3 + ____ O2

Type of reaction: ______

6) ____ NH3 + ____ I2 à ____ N2I6 + ____ H2

Type of reaction: ______

7) ____ H2O + ____ SO3 à ____ H2SO4

Type of reaction: ______

8) ____ H2SO4 + ____ NH4OH à ____ H2O + ____ (NH4)2SO4

Type of reaction: ______

For the following reactions, indicate the type of reaction occurring:

Reactivity Series and Solubility Problems

Determine the products of the following reactions, label the states of all products, and balance each equation.

a) Cu (s) + Ag(NO3) (aq) à

b) Fe(s) + CuCl2 (aq) à

c) Pb(NO3)2 (aq) + K2Cr2O7 (aq) à

d) Pb(NO3)2 (aq) + KI (aq) à

e) Na2CO3 (aq) + Ag(NO3) (aq) à

f) HCl (aq) + Ag(NO3) (aq) à

g) KI (aq) + Ag(NO3) (aq) à

h) Na2CO3 (aq) + HCl (aq) à

i) K2Cr2O7 (aq) + Ag(NO3) (aq) à

j) Pb (s) + Cu(NO3)2 (aq) à

k) Cu (s) + Pb(NO3)2 (aq) à

l) AlCl3 (aq) + Zn (s) à

m) KCl (aq) + H2 (g) à

n) KCl (aq) + F2 (g) à

o) Br2 (g) + PbI2 (aq) à

p) CaCl2 (aq) + H2SO4 (aq) à

q) H3PO4 (aq) + (NH4)I (aq) à

r) MgS (aq) + B(NO3)3 (aq) à

s) H(OH) (aq) + BaBr2 (aq) à

t) Pb(NO3)2 (aq) + Li2(SO4) (aq) à

u) (NH4)2S (aq) + Sr(OH)2 (aq) à

Formula, Total Ionic, and Net Ionic Equations – Practice Problems

Write a balanced formula unit, total ionic, and net ionic equation for the following reactions. Assume all reactions occur in water or in contact with water.

1. acetic acid + sodium hydroxide à

2. calcium hydroxide + hydrosulfuric acid à

3. Ba(NO3)2 + K2CO3 à

4. lead (II) hydroxide + carbonic acid à

5. Our bones are mostly calcium phosphate. Calcium chloride reacts with potassium phosphate to form calcium phosphate and potassium chloride.

Package Review Questions

1.  Say whether or not a precipitate will form when the following aqueous solutions are mixed.

a)  Sodium sulphate solution and lead nitrate solution

b)  Copper (II) chloride solution and sodium hydroxide solution

c)  Potassium nitrate solution and sodium chloride solution

d)  Potassium phosphate solution and nickel nitrate solution

2.  Write the balanced equation for the double displacement reactions that occur when aqueous solutions of the following ionic salts are mixed.

a)  Lead (II) nitrate and sodium iodide

b)  Iron (III) nitrate and potassium hydroxide

c)  Silver nitrate and copper (II) chloride

d)  Sodium phosphate and zinc nitrate

e)  Barium nitrate and sulphuric acid

3.  Write the net ionic equations for the precipitation reactions that occur when aqueous solutions of the following ionic salts are mixed.

a)  Potassium phosphate and zinc nitrate

b)  Calcium nitrate and zinc phosphate

c)  Sodium sulphide and aluminum nitrate

d)  Lead (II) nitrate and calcium chloride

e)  Hydrochloric acid and silver nitrate solution