Chemical Reactions - 11-12

Chemical Reactions

Third Quarter

All chemical reactions involve change in substances.

A substance that undergoes a chemical reaction is called a REACTANT.A substance that is produced in a chemical reaction is called a PRODUCT.

REACTANTS

PRODUCTS

A CHEMICAL EQUATION is a short way describing a chemical reaction in which symbols of the elements and the formulas of

compounds represent the change.

Ex. Combination of Carbon and Oxygen to form Carbon dioxide is written as

C (s) + O2

(g)

CO2 (g)

Some Symbols Used in Writing Chemical Equations

Symbol Meaning

+ Separate two or more formulas

Yield(s) or Produce(s)

(s) or Solid or Formation of precipitate

(l) Liquid

(g) or Gas or Evolution of Gas

(aq) Aqueous

Heat is supplied

Catalyst is used

cat

In some reaction, catalyst is used. A catalysts is a substance that hastens a reaction without being used up

Ex. Manganese (II) Oxide as catalyst to decompose aqueous hydrogen peroxide, producing oxygen gas and liquid water.

2H2O2

(aq)

O2 (g) + 2H2O (l)

MnO

Inhibitors – slows down chemical changes

When you heat a small amount of mercury (II) oxide in a test tube, the amorphous orange compound turns brown, then black, and finally disappears. Moisture is also observed near the mouth of the test tube. The grayish substance left clinging at the middle portion of the test tube is mercury, and the smoke seen is oxygen.

Mercury (II) Oxide

Mercury and Oxygen

Heat

The word equation therefore is as follows:

Word equation changed into symbols and formula to give the chemical equation:

HgO Hg + O2

The chemical change that occurs when a strip of magnesium metal is burned in air to produce magnesium oxide.

Magnesium + Oxygen

GasMagnesium Oxide

Heat

The word equation therefore is as follows:

Word equation changed into symbols and formula to give the chemical equation:Mg (s) +

O2(g) MgO (s)

The guiding principle used in balancing chemical equations: “LAW OF CONSERVATION OF MASS”- Atoms are neither created nor destroyed but merely rearranged during a chemical change.

A balanced chemical reaction must include same number of each kind of atoms on both sides of the equation:Mg (s) +

O2(g) MgO (s)2 2

oThe number is called COEFFICIENT. oIt serves as multiplier for the whole formula

that

A undergoes

substance

a

reactionchemical

that

A

producedsubstance

is

reaction

chemical

in

a

a

course

Chemist’s

The

the

for

of

shorthanddescribin

gchemical

reaction

GOAL

• write chemical equations from descriptions of chemical reactions using appropriate symbols;

• balance simple chemical equations based on the law of conservation of mass;

1. When dissolved beryllium chloride reacts with dissolved silver nitrate in water, aqueous beryllium nitrate and silver chloride powder was made.

BeCl2(aq) + AgNO3(aq) Be(NO3)2(aq) + AgCl(s)

BeCl2(aq) + 2 AgNO3(aq) Be(NO3)2(aq) + 2 AgCl(s)

2. When isopropanol (C3H8O) burns in oxygen. Carbon dioxide, water, and heat are produced.

C3H8O(l) + O2(g) CO2(g) + H2O(g)

2 C3H8O(l) + 9 O2(g) 6 CO2(g) + 8 H2O(g)

Cleansing surgeons hands

and instruments

Disinfection of skin

3. When dissolved sodium hydroxide reacts with sulfuric acid, aqueous sodium sulfate, water, and heat are formed.

NaOH(aq) + H2SO4(l) Na2SO4(aq) + H2O(l)2 NaOH(aq) + H2SO4(l) Na2SO4(aq) + 2 H2O(l)

Cleaning agentFood

preparation

4. Plants carry out photosynthesis—the creation of glucose and oxygen from carbon dioxide, water and sunlight;

CO2 (g) + H2O (l) C6H12O6 (s) + O2 (g)

6CO2 (g) + 6H2O (l) C6H12O6 (s) + 6O2 (g)

Self - Reflection

• What questions and uncertainties do you still have about chemical reactions?

• How does what you have learned changed your thinking?

4. When fluorine gas is put into contact with calcium metal at high temperatures, calcium fluoride powder is created in an exothermic reaction.

F2(g) + Ca(s) CaF2(s)

F2(g) + Ca(s) CaF2(s)

5. When sodium metal reacts with iron (II) chloride, iron metal and sodium chloride are formed.

Na(s) + FeCl2(s) NaCl(s) + Fe(s)

2 Na(s) + FeCl2(s) 2 NaCl(s) + Fe(s)

6. Magnesium metal reacts with nickel (III) nitrate to form magnesium nitrate and nickel

metal.

Mg + Ni(NO3)3 Mg(NO3)2 + Ni

2Mg + 3Ni(NO3)3 2Mg(NO3)2 + 3Ni

7. Copper and sulfuric acid react to form copper (II) sulfate and water and sulfur dioxide.

Cu + H2SO4 CuSO4 + H2O + SO2

Cu + 2 H2SO4 CuSO4 + 2 H2O + SO2

8. Calcium hydroxide and phosphoric acid (H3PO4) react to

form calcium phosphate and water.

Ca(OH)2 + H3PO4 Ca3(PO4)2 + H2O

3 Ca(OH)2 + 2 H3PO4 Ca3(PO4)2 + 6 H2O

9. Sodium phosphate and calcium chloride react to form calcium phosphate and sodium

chloride.

Na3PO4 + CaCl2 NaCl + Ca3(PO4)2

2 Na3PO4 + 3 CaCl2 6 NaCl + Ca3(PO4)2

10. Aluminum bromide and chlorine gas react to form aluminum chloride and

bromine gas.

AlBr3 + Cl2 AlCl3 + Br2

2 AlBr3 + 3 Cl2 2 AlCl3 + 3 Br2