Representing reactions- IGCSE CHEMISTRY WORK SHEETS AND NOTES

Word equationsIf a reaction occurs between magnesium and oxygen, magnesium oxide is produced, here is the word equation for this reaction:

magnesium + oxygen --> magnesium oxide

Some other examples are:

hydrochloric acid + calcium carbonate --> calcium chloride+ carbon dioxide+ water sodium + water --> sodium hydroxide + hydrogen

hydrochloric acid + sodium hydroxide --> sodium chloride + water

Write word equations for the reactions in which the following compounds form from a halogen and another suitable element: hydrogen fluoride, hydrogen chloride, iron III chloride, iron III bromide, sodium chloride, copper chloride.

formulaeThe formula of an element or compound is simply the symbol of each element present and numbers to show how many atoms are present. Carbon dioxide has the formula CO2. This means that it has one carbon atom and two oxygen atoms in each molecule

Use valency to work out the formulae of the following compounds: sodium chloride, potassium bromide, magnesium oxide, calcium sulphide, aluminium nitride, calcium iodide, lithium oxide, aluminium chloride, aluminium sulphide, magnesium nitride.

Calculating relative formula massAdd up the relative atomic mass (found in periodic table) of each atom in the compound.

e.g. Al203 relative atomic masses of Al = 27, O = 16 (found in periodic table).

The formula shows 2 atoms of aluminium and 3 atoms of oxygen so:

formula mass of = (2*27) + (3*16) =54 + 48 = 102

Work out the relative formula masses of the following:

MgO, FeS, O2, H2O, CaBr2, Na2S, CaCO3, NaOH, HCl, (NH4)2SO4.
Relative atomic masses Mg=24, O=16, Fe=56, S=32, Ca=40, Br=80, C=12, Na=23, H=1, Cl=35.5.
Simple balanced equationsIt is possible to write balanced equations for reactions. For example substances such as hydrogen and magnesium combine with oxygen. One method to write them is:Write a word equation first.
Magnesium + oxygen --> magnesium oxide
Write in the formulae of the substances used.
Mg + O2 --> MgO
Balance the equation so that each element has the same number of atoms on each side.
2Mg + O2 --> 2MgO
sodium + oxygen --> sodium oxide
4Na{s} + O2{g} --> 2Na2O{s}
(word equation) hydrogen + oxygen ---> water(formulae)
H2 + O2 -----> H2O(balance)
2H2 + O2 -----> 2H2O


State symbolsThe state symbols are put in a balanced equation to show whether something is a solid, liquid, gas or dissolved in water (aqueous solution). The symbols for these are:
state
Symbol
Solid (s)
Liquid (l)
Gas (g)
Aqueous (aq)
Magnesium + oxygen --> magnesium oxide 2Mg{s} + O2{g} --> 2MgO{s} hydrochloric acid + calcium carbonate --> calcium chloride + carbon dioxide + water2HCl (aq) + CaCO3 ---> CaCl2(aq) + CO2(aq) + H20(l)

Task

Balanced equations and ionic equations

Ionic equations only show ions which change in a reaction and ignore those which do not change.

E.g.word equation
hydrochloric acid + sodium hydroxide --> sodium chloride + water

balanced chemical equation

HCl(aq) + NaOH(aq) ---> NaCl(aq) + H2O(l)

ionic equation

H+(aq) + OH-(aq) ---> H2O(l)

E.g. in the electrolysis of sodium chlorideCl-(aq) --> Cl(g) + e-2Cl(g) --> Cl2(g)

Working out formulae from reacting masseselements reacting magnesium chlorine

symbols of elements Mg Clmasses reacting (from experiment)
2.4g 7.1gmolar mass (look up relative atomic 24g/mol 35.5g/molmass in periodic table)amounts (amount = mass/molar mass) 2.4g/24g/mol 7.1g/35.5g/mol = 0.1mol 0.2molratio of atoms (divide by smallest) 1 : 2formula MgCl2



Task :

Work out formulae of compounds formed when the following react:56g of iron and 32g of sulphur (Fe =56, S =32)2g of hydrogen and 16g of oxygen (H=1, O=16)14g of lithium and 16g of oxygen (Li=7)32g of copper and 8g of oxygen (Cu=64)6.4g of copper and 0.8g of oxygen.

Calculating reacting masses using equationsYou can work out ratio of the masses of products and reactants by simply multiplying the number of moles shown in the equation by the formula mass of each substance.

Example 1: What mass of magnesium oxide can be made from 12g of magnesium? Relative atomic masses are Mg =24, O = 16.

equation 2Mg(s) + O2(g) --> 2MgO(s)

formula 2*24 1(16*2) 2(24+16)

masses =48 =32 =80 reacting 48g of Mg forms 80g of MgOmasses 1g of Mg forms 80/48 g of MgO 12g of Mg forms 12*80/48 g of MgO = 20g

Example 2: What mass of magnesium oxide can be made from 12g of magnesium?

equation 2Mg(s) + O2(g) --> 2MgO(s)

amounts 2 moles 1 mole 2 moles masses 2*24 1{16*2} 2{24+16} =48g =32g =80g

so 48g Mg forms 80g MgO 1g Mg forms 80/48 g MgO 12g Mg forms 12*80/48 g MgO = 20g Also note that the ratio of amounts of reactants and products in the equation above can be written as:

Amount of Mg/amount of O2 =2/1 Or Amount of O2/amount of MgO = 1/2


Task : problem C2.08 You decide to travel from London to Delhi for a holiday and hire your own Airbus 319 jet. You fly the 2183 miles to Cairo first and make 9.4 tons of carbon dioxide.


After seeing the Pryramids you fly the 1018 miles to Riyadh making 4.5 tons of carbon dioxide. After a brief stop in the Saudi Capital you fly on the 1900 miles to Delhi making 8.1 tons of carbon dioxide.


Finally you return to London travelling 4171 miles and releasing 22 tons of carbon dioxide. The jet burns the fuel kerosine

C15H32 in the reactionC15H32 + 23O2 --> 15CO2 +16H2O(a)

How much carbon dioxide was released into the atmosphere during the trip?(b) What mass of kerosine was burnt?

(c) What effect does the trip have of the environment?

Alkanes- As level work sheet

Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet.

1. One of the terminal steps in the photochemical chlorination of methane is:
A Cl2---------- 2Cl•
B CH3• + CH3• ---CH3 CH3
C CH4 + Cl--- CH3Cl + H+
D CH4 + Cl•-- CH3 + HCl

2. Which one of the following represents a propagation step in the chlorination of methane?
A CH4 + Cl2 -- CH3Cl + HCl
B CH4 + Cl• --- CH3• + HCl
C Cl2 ---- 2Cl•
D CH3• + Cl• --- CH3Cl

3. Which one of the following species is not formed in the photochemical reaction between chlorine and methane?
A H•
B Cl•
C HCl
D CH3CH3

4. Which one of the following is formed in the initiation step in the mechanism of the chlorination of methane?
A chlorine atoms
B hydrogen atoms
C hydrogen chloride
D methyl radicals


5. 10 cm3 of an equimolar mixture of hydrogen and methane were combusted by exploding with 25 cm3 of pure oxygen. All volume measurements were made at 20oC and 1 atmosphere pressure.

The volume of the mixture (in cm3 ) after the explosion was:
A 12.5
B 15
C 17.5
D 20
Section B

Answer all questions

1. Methane reacts with chlorine in the presence of ultraviolet light, the reaction occurring in a series of steps.

(a) The initiation step involves the action of ultraviolet light on chlorine gas.

Write an equation and explain what happens to the chlorine.

equation


explanation

(b) Write two equations for the second step in this mechanism.

1.

2.


(c) Suggest why traces of ethane are found in the product mixture.
2. (a) Kerosene, which contains a mixture of C11 and C12 hydrocarbons, is obtained from crude oil by fractional distillation. Explain the term fractional distillation.

(b) The hydrocarbons from kerosene can be cracked to form other useful products.

(i) Explain the term cracking.

(ii) Using the molecule C11H24, write an equation to illustrate cracking.

(c) Another fraction contains several isomers of C7H16. Draw structures and give systematic names for any two branched chain isomers of C7H16.

Structure (i)
Name
Structure (ii)

(d) Hexane is exploded in the internal combustion engine according to the equation
2C6H14 + 19O2 12CO2 + 14H2O

3.Calculate the molar enthalpy of combustion of C6H14 using the
bond enthalpies given.

kJ mol-1
C-C 346
C-H 413
0-H 453
0=0 490
C=0 740