V. Listening

a. Guess the meaning of the following words and match them with their definitions. Then listen to the tape and check your guesses:

1) to denote a) a substance that takes part in and undergoes

change during a reaction

2) ratio b) … tells you what happens in a chemical reaction

3) reactant c) to represent something

4) equation d) the quantitative relation between two amounts 

b. Listen to the tape and complete the sentences using the words from ex. Va.

1. The molecular formula ………… the molecular mass of the chemical substance.

2. The empirical formula gives the simplest whole number ………. of atoms of different elements present in a molecule.

3. According to the Law of Conservation of Mass the changes in …………. and products must always be balanced before and after the reaction.

4. The Hit and Trial Method is used for simple ……… .

c. Listen to the tape and mark the sentences as true or false.

1. A chemical formula represents the composition and the number of elements. T/F

2. Small molecules of ionic and network compounds are best described by the empirical formula. T/F

3. The empirical formula will always be a whole number multiple of the molecular formula. T/F

4. A chemical equation represents a chemical reaction. T/F

5. The Partial Equation Method is used for complex equations having many reactants and products. T/F

VI. Extra activities

a. Study the rules of reading formulas and equations and try to remember them.

Буквы латинского алфавита, обозначающие название элементов, читаются согласно английским названиям букв алфавита.

Знак + читается plus, and, together, with, reacts with.

Знак - обозначает одну связь или единицу родства и не читается.

Знак = читается gives, forms, produces.

Знак → читается gives, passes over or leads to.

Знак ↔ читается forms and is formed from.

Цифра перед названием элемента обозначает число молекул.

Examples:

1) C + O₂ → CO₂ – 1 atom of carbon reacts with one 1 two-atom molecule of oxygen and produces 1 molecule of carbon dioxide.

2)2H₂ + O₂ → 2H₂O – two molecules of H two plus O two gives two molecules of H two O.

3) N₂ + 3H₂ ↔ 2NH₃ – N two plus three molecules of H two form and are formed from two molecules of NH three.

4) CH₄₊2O₂→CO+ 2H₂O – CH four plus two molecules of O two gives CO plus two molecules of H two O

5) H⁺+NaHCO₃→Na⁺+H₂CO₃→Na⁺+H₂O+CO₂ – hydrogen ion plus NAHCO three gives natrium ion plus H two O plus CO two

6)4HCl+O₂=2Cl₂+2H₂O – four molecules of HCL plus O two gives two molecules of CL and two molecules of H two O

7) AcOH ↔ AcO^-+H⁺– ACOH forms and is formed from AC oxygen plus hydrogen ion

AcO^-– acyloxy ion

b. Read the equation using the verbs: to give, to react, to interact, to be equal to, to be, to run, to yield, to produce, to make.

1. 4HC1 + О2 =2Cl2+ 2H2O

2. CaSO4×2H2O →CaSO4+ 2H2O

3. СuCl₂+ Zn= ZnCl₂ + Сu  

4. N₂ + О₂ →N₂О₃

5. 2KMnO₄   = К₂МnO₄ + MnO₂ + O₂  

6. СаCl₂ + Nа₂СО₃ → СаСО₃ + NаCl