Сhemical reaction

Class:

7В

Date: 13.03.18

Subject matter:

Chemistry

Theme:

Сhemical reaction

Purpose of the lesson:

The concept of connection, substitution, loss and exchange reactions, their ability to distinguish between their chemical equations

Visibility:

Periodic table, active board, computer, power point, video

Method:

Explain, ask questions

Course progress:

TYPES OF CHEMICAL REACTIONS

Chemical reactions are changes in which new substances are formed. During these changes, substances may break down into simpler substances or may exchange parts. Additionally, some substances may combine to yield a more complex substance. Chemical reactions can be classified as follows: combination, decomposition, single displacement, double displacement, combustion, endothermic and exothermic reactions.

COMBINATION REACTIONS

Reactions in which simpler substances combine to make a more complex one is called combination reaction.

Combination reactions can be illustrated as:

Example:

Other examples:

S + O₂ → SO₂

2SO₂ + O₂ → 2SO₃

SO₃ + H₂O → H₂SO₄

Write and balance the equations for the reactions of lithium, aluminum and calcium with oxygen.

When these elements react with oxygen, oxides of the elements will be produced, Li₂O, Al₂O₃ and CaO. Balanced equations for the formations of these compounds are:

4Li + O₂ → 2Li₂O

4Al + 3O₂ → 2Al₂O₃

2Ca + O₂ → 2CaO

DECOMPOSITION REACTIONS

Reaction in which complex substance breaks down to simpler substance is called decomposition reaction.

Decomposition reaction can be illustrated as:

Example:

Other examples:

2H₂O_(l) → 2H_2(g) + O_2(g)

2KClO₃→ 2KCl + 3O₂

2NaCl_(l) → 2Na_(l) + Cl_2(g)

2Ag₂O → 4Ag + O₂

SINGLE DISPLACEMENT REACTIONS

Reactions in which one element displaces another one are called single displacement reactions.

Single displacement reactions can be illustrated as:

Zn_(s) + CuSO_4(aq) → Cu_(s) + ZnSO_4(aq)

Zinc + Copper (II) sulfate → Copper + Zinc sulfate

NiO_(s) + C_(s) → Ni_(s) + CO_(g)

Cu₂O_(s) + CO_(g) → 2Cu_(s) + CO_2(g)

However, if you immerse another piece of zinc into sodium chloride solution, no

reaction will take place, because zinc is less active than sodium:

Zn_(s) + NaCl_(aq) ⎯⎯→ no reaction

Such single displacement reactions may also take place between nonmetals. For example, chlorine is more active than bromine, so chlorine may react with sodium bromide:

2NaBr_(aq) + Cl_2(g) → 2NaCl_(aq) + Br_2(l)

Complete and balance the following equations:

a. MgO + C →

b. Al₂O₃ + H₂ →

c. PbO + CO →

d. Ba + H₂O →

DOUBLE DISPLACEMENT REACTION

In a double displacement reaction, two parts in different compounds displace to form two new compounds. In such reactions, two reactants yield two products. Double displacement reaction can be illustrated as:

KCl_(aq) + AgNO_3(aq) → KNO_3(aq) + AgCl_(s)

Potassium chloride + Silver nitrate → Potassium nitrate + Silver chloride

COMBUSTION REACTIONS

Combustion reaction is a chemical reaction between substances, usually including oxygen and usually accompanied by the generation of heat and light in the form of flame.

Example:

CH₄ + O₂ → CO₂ + H₂O

C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

EXOTHERMIC REACTIONS

In this type of chemical reaction, energy is produced as heat, and is noted on the products’ side (right).

For instance, the burning of coal produces a quantity of energy, which is released as heat. The reaction is written as;

C_{(graphite)(s)} + O_2(g) → CO_2(g) + 393.5 Kj

ENDOTHERMIC REACTIONS

In an endothermic reaction, heat is absorbed. In this type of reaction equation, heat is noted on the reactants’ side (left).

Decomposition of CaCO₃ is a good example of an endothermic reaction, where its equation is expressed as follows:

CaCO_3(s) + 169.5 kJ → CaO_(s) + CO_2(g)

Indicate the following reactions as endothermic or exothermic reactions:

a. 2Al_(s) + Fe₂O_3(s) → 2Fe_(s) + Al₂O_3(s) + 850 kJ

b. H_2(g) + I_2(g) + 54 kJ → 2HI_(g)

c. CO_(g) + 1/2O_2(g) → CO_2(g) + heat

d. CO_2(g) + 2H₂O_(l) + heat → CH_4(g) + 2O_2(g)

e. N₂O_(g) + H_2(g) → N_2(g) + H₂O_(l) + energy

Approving Lesson:

Questions:

1. What types of reactions will you have?

2. An example is the combustion reaction.

3. What is a chemical reaction?