Lecture No. 4Chemical reactions and

chemical equationsLecturer:

Amal Abu- Mostafa

How to recognize which type of chemical

reactions.

Balancing chemical equation.

Calculation based on chemical equation.

Session Objectives:

Look at the reactants and products Element(E), Compound(C)

E + E → C Synthesis C → E + E Decomposition E + C → E + C Single replacement C + C → C + C Double

replacement Acid+Base → H2O + Salt Acid/Base

reaction (Double replacement)

CxHy + O2 → CO2 + H2O (Look at the Products)

Combustion

How to recognize which type of chemical reactions

H2 + O2 → Synthesis H2O → Decomposition AgNO3 + NaCl → Double replacement Zn + H2SO4 → Single replacement HgO → Decomposition NaCl(s) + F2(g) → Single replacement KBr +Cl2 → Single replacement Mg(OH)2 + H2SO4 → Double replacement (Acid/Base) HNO3 + KOH → Double replacement (Acid/Base)

Examples

Zn + O2 ® Synthesis

HgO + Pb® Single replacement HBr + NH4OH ®Double

replacement Cu(OH)2 + KClO3 ® Double

replacement AgBr + Cl2 ®Single replacement

CaPO4 ®Decomposition

Examples

When the coefficients in a chemical equation are correctly given, the numbers of atoms of each element are equal on both sides of the arrow, none are destroyed and none are created. The equation is then said to be balanced.

Important rule: Balance first the atoms for elements that occur in only one substance on each side of the equation.

BALANCING CHEMICAL EQUATION:

As an example, consider the burning of propane gas:

C3H8 + O2 CO2 + H2O (this equation is not balanced).

First C atoms: 1C3H8 + O2 3CO2 + H2O Second H atoms: 1C3H8 + O2 3CO2 + 4 H2O Third O atoms: 1C3H8 + 5 O2 3CO2 + 4 H2O

How to balance this equation:

A) HCl + Na2CO3→NaCl + CO2 + H2O 2HCl + Na2CO3→2NaCl + CO2 + H2O

B) balance C and H then O 1) CH4 + O2 CO2 + H2O CH4 + 2O2 CO2 + 2H2O

2) C8H18 + O2 → CO2 + H2O C8H18 + 25/2 O2 → 8 CO2 + 9 H2O 2 C8H18 + 25 O2 → 16 CO2 + 18 H2O

Balance these equations:

H3PO3 → H3PO4 + PH3

Solution: Oxygen occurs in just one of the products (H3PO4). So

it is therefore easiest to balance O atoms first. 4H3PO3 → 3H3PO4 + PH3

This equation is now also balanced in P and H atoms. Thus, the balanced equation is

4H3PO3 → 3H3PO4 + PH3

Balance this equations:

To answer quantitative questions, you must first look at the balanced chemical equation, for example:

N2(g) + 3H2(g) → 2NH3(g)

1molecule N2 + 3 molecules H2 → 2molecules NH3

1 mol N2 + 3 mol H2 → 2 mol NH3

(1×28) g N2 + (3 × 2) g H2 → (2 × 17 )g NH3

CALCULATION BASED ON CHEMICAL EQUATION:

Example 1 : A)How many moles of O2 are needed to burn 1.8 mol of

C2H5OH in the equation? B)And How many moles of CO2 produced when 0.274

mol C2H5OH burned in this example?

C2H5OH + 3O2 → 2CO2 + 3H2O Solution: (A) from the equation: 1mol of C2H5OH needs → 3 mol of O2 to be burned 1.8 mol of C2H5OH needs → ??? Moles of O2

moles of O2= 1.8 × 3 = 5.4 mol 1

CALCULATION BASED ON CHEMICAL EQUATION:

1mol of C2H5OH produces → 2 mol of CO2

0.274 mol of C2H5OH produces → ?? Moles of CO2

Moles of CO2 = 0.274 × 2 = 0.548 mol

1

Solution: (B) from the equation:

A) How many gm of O2 are required to react with 0.3 mol Al in the reaction

4 Al + 3 O2 → 2 Al2O3

Solution: First we find how many moles of O2 are required to react with 0.3 mol Al in the reaction.

4 mol of Al → 3 mol of O2 are required

0.3 mol of Al → ?? mol of O2 are required moles of O2 = 0.3 × 3 = 0.225 mol 4 Mass of O2 = n × M = 0.225× 32= 7.2 g

Example 2:

B) How many gram of Al2O3 could be formed if 12.5 g O2 react completely with Al?

4 Al + 3 O2 → 2 Al2O3

Solution: Moles of O2 = m = 12.5 = 0.391 mol M 32

Example 2:

From the equation: 3 mol of O2 → 2 mol of Al2O3

0.391 mol of O2 → ?? Moles of Al2O3

Moles of Al2O3 = 0.391× 2= 0.26 mol 3 MASS OF Al2O3 (m) = n × M= 0.26 × 102 =26.6 g

Thank you