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- Concepts:
- atom, molecule, diatomic molecule, symbol, formula,
- chemical change, subscript, coefficient, equation, chemical (symbol)
equation, balanced word equation, balanced chemical equation
- reactant, product,
- Skills:
- State that a chemical reaction is the same as a chemical change
- Construct word equations and simple balanced chemical equations for
combination reactions when given relevant information
- Use the symbols of the elements and write the formulae of simple
compound
- deduce the formula of a simple compound from the relative numbers of
atoms present
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- deduce the formula of a simple compound from a model or a diagrammatic
representation
- construct word equations and chemical equation (using chemical
formulas) for a chemical reaction given relevant information
- Describe how to balance a chemical equation and that this is necessary
in order for the reaction to obey the law of conservation of mass (in
relation to atoms, molecules, and moles)
- Balance simple chemical equations
- Explain the importance of the subscripts, coefficients, and symbols
used in a chemical equation
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- 2H2 (g) + O2 (g) ® 2H2O(g)
- reactants product(s)
- The above equation is an example of a balanced chemical equation.
- “+” means “reacts with”
- the coefficients show the relative quantity of atoms or molecules of
the reactants and products (1 being understood)
- the symbols inside the brackets indicate the physical state of the pure
substances except “aq” which means aqueous, in solution (dissolved in
water)
- “s” indicates solid, “l” indicates liquid and “g” indicates gaseous
- A balanced chemical equation shows the same type and equal number of
atoms and charges on both sides.
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- So a reaction between zinc and iodine can be visualized as follows:
- Zinc + Iodine à zinc iodide
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- 2H2 (g) + O2 (g) ® 2H2O(g)
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- Other reactions are:
- carbon + oxygen à carbon dioxide
- This is the reaction that takes place when coal burns.
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- hydrogen + chlorine à
hydrogen chloride
- hydrogen + bromine à
hydrogen bromide
- hydrogen + iodine à
hydrogen iodide
- sulfur + oxygen à sulfur
dioxide
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- Metal with air (oxygen) – combustion reaction
- Magnesium + oxygen ®
magnesium oxide
- Mg (s) + O2
(g) ® MgO (s)
- Zinc + oxygen ® zinc oxide
- Zn (s) + O2
(g) ® ZnO (s)
- Sodium + oxygen ® sodium
oxide
- Na (s) + O2
(g) ® Na2O
(s)
- Aluminum + oxygen ® aluminum
oxide
- Al (s) + O2
(g) ® Al2O3 (s)
- In general then,
- Metal (s) + oxygen (g) ® metal oxide (s)
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- Non-metal and oxygen – combustion reaction
- Carbon (s) + Oxygen (g) ® carbon dioxide (g)
- C (s) + O2 (g) ® CO2 (g)
- Sulfur (s) + Oxygen (g) ® sulfur dioxide (g)
- S (s) + O2 (g) ® SO2 (g)
- Hydrogen (g) + Oxygen (g) ® water (l)
- H2 (s) + O2 (g) ®
H2O (g)
- In general then,
- Non-metal + oxygen (g) ® non-metal oxide
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- Metal with hydrogen
- Sodium + hydrogen ® sodium
hydride
- Na(s) + H2 (g)
® NaH(s)
- Lithium + hydrogen ® Lithium
hydride
- Li(s) + H2 (g) ® LiH(s)
- Magnesium + hydrogen ®
potassium hydride
- Mg(s) + H2 (g) ® MgH2(s)
- In general then,
- Metal + hydrogen ® metal
hydride
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- Metal with halogen
- Sodium + chlorine ® sodium
chloride
- Na(s) + Cl2
(g) ® NaCl(s)
- Sodium + bromine ® sodium
bromide
- Na(s) + Br2
(l) ® NaBr(s)
- Lithium + iodine ® Lithium
iodide
- Li(s) + I2 (s)
® LiI(s)
- Potassium + fluorine ®
potassium fluoride
- K(s) + F2 (g)
® KF(s)
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- Magnesium + Iodine ®
Magnesium iodide
- Mg(s) + I2 (s)
® MgI2(s)
- Calcium + chlorine ® Calcium
chloride
- Ca(s) + Cl2
(g) ® CaCl2(s)
- Aluminum + Bromine ®
Aluminum bromide
- Al(s) + Br2
(l) ® AlBr3(s)
- Zinc + Iodine ® zinc iodide
- Zn(s) + I2 (s)
® ZnI2(s)
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- Non-metal (hydrogen) with halogen
- Hydrogen + chlorine ®
hydrogen chloride
- H2 (g) + Cl2
(g) ® HCl (g)
- Hydrogen + iodine ® hydrogen
iodide
- H2 (g) + I2 (g)
® HI (g)
- Hydrogen + bromine ®
hydrogen bromide
- H2 (g) + Br2
(g) ® HBr (g)
- In general then,
- Metal/nonmetal + halogen ®
metal/nonmetal halide
- (Compounds of halogen are called halides.)
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- You should have noted by now that
- Oxygen becomes oxide.
- And compounds containing oxygen and another element are referred to as
oxides.
- Nitrogen becomes nitride.
- Similarly compounds containing nitrogen and another element are
referred to as nitrides.
- Chlorine becomes chloride, and compounds containing chlorine and
another element are referred to as chlorides.
- Bromine becomes bromide, and these binary compounds (compounds made up
of only two elements) are referred to as bromides.
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- Iodine becomes iodide, and these binary compounds are referred to as
iodides.
- Fluorine becomes fluoride, and these binary compounds are referred to
as fuorides.
- Similarly:
- Phosphorus becomes phosphide, and these binary compounds are referred
to as phosphides.
- Sulfur becomes sulfide, and lastly these binary compounds are referred
to as sulfides.
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- 2H2 (g) + O2 (g) ® 2H2O(g)
- reactants product(s)
- The above equation is an example of a balanced chemical equation.
- A balanced chemical equation shows the same type and equal number of
atoms and equal charges on both sides
- A chemical equation must be balanced because atoms can neither be
created nor destroyed, which follows from the law of conservation of
mass.
- So it would be wrong and misleading for a chemical balance sheet which
is what a chemical equation is, to show the creation or destruction of
atoms!!
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- CH4 + O2 ® CO2 + H2O
- A chemical equation is balanced by adding coefficients in front of the
chemicals.
- 1. Begin by balancing elements that occur in only one substance on each
side
- In this example C or H.
- C is already balanced and there are 4 H on the left but only 2 on the
right.
- The number of H atoms on the right can be increased to 4 by multiplying
it by 2 (by adding the coefficient 2).
- Add 2 in front of H2O (and not change H2O to H4O).
- CH4 + O2 ® CO2 + 2H2O
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- CH4 (g) + O2 (g)
® CO2 (g) + 2H2O(g)
- 2. Balance others leaving the element that occurs by itself last.
- In this example C or H, depending on which you started with, and then
finally oxygen.
- Since we started with C and then moved on to H, we have only O to
balance.
- There are 2 O atoms on the left but 4 O atoms on the right, and just as
with H, we can multiply O2 by 2 to raise the number of O
atoms on the left to 4.
- CH4 + 2O2 ® CO2 + 2H2O
- Notice balancing the element (here O2) that occurs by
itselft last does not change the number of other already-balanced atoms
in the reaction.
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- 3. Indicate physical state of the chemicals.
- CH4 (g) + 2O2 (g) ® CO2 (g) + 2H2O(g)
- The equation is balanced.
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- Which way will the seesaw tilt?
- What must you do to balance the seesaw?
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- 1. Balance the following equations.
- a) Zinc + hydrochloric acid ® zinc chloride + Hydrogen
- __ Zn (s) + __ HCl (aq)
® __ ZnCl2 (aq) + __ H2 (g)
- b) Sodium oxide + sulfuric acid à sodium sulfate + water
- __ Na2O (s) +
__ H2SO4 (aq) ®
__ Na2SO4 (aq) + __ H2O
(l)
- c) copper oxide + hydrochloric acid à copper(II) chloride + water
- __ CuO (s) + __ HCl (aq)
® __ CuCl2 (aq)
+ __ H2O (l)
- d) Zinc oxide + sulfuric acid à zinc sulfate + water
- __ ZnO (s) + __ H2SO4
(aq) ® __ ZnSO4 (aq)
+ __ H2O (l)
- e) Sodium hydroxide + sulfuric acid à sodium sulfate + water
- __ NaOH (aq) + __ H2SO4
(aq) ® __ Na2SO4 (aq)
+ __ H2O (l)
- f) Barium hydroxide + hydrochloric acid à barium chloride + water
- __ Ba(OH)2 (aq) + __ HCl (aq) ®
__ BaCl2 (aq) + __ H2O (l)
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- 2. Balance the following equations.
- H2 (g) + O2
(g) ® H2O (l)
- H2 (g) + Br2
(g) ® HBr (g)
- K (s) + O2 (g) ® K2O (s)
- CO (g) + O2
(g) ® CO2 (g)
- Na (s) + CuCl2
(aq) ® NaCl (aq) + Cu (s)
- Zn (s) + HCl (aq) ® ZnCl2
(aq) + H2 (g)
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- 1. N04/1/9 When propane is burned, carbon dioxide and water are formed,
as shown.
- C3H8 + 5O2 ® r CO2 + s H2O
- Which values of r and s balance the equation?
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- 3. The diagrams show the arrangement of particles in the three states of
matter.
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- 4. The equation shows the reaction between hydrogen molecules and
chlorine molecules.
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- 5. Which diagram shows molecules of a compound containing twice as many
nitrogen atoms as oxygen atoms?
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- 6. A molecule of compound X contains the following.
- 2 atoms of carbon, C
- 2 atoms of oxygen, O
- 4 atoms of hydrogen, H
- What is the formula of X?
- A. (CH2)2O B. (CH2)2O2
C. C2(OH)4 D. C4H2O
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- 1. J04/2/1.The diagram shows models of various structures,
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- Which three of the structures A to F represent elements? Give a reason
for your answer. [2]
- (b) Which one of the structures A to F represents a gas containing
single atoms? [1]
- (c) (i) Which one of the structures A to F represents a gas containing
diatomic molecules? [1]
- (ii) State the name of a gas which has diatomic molecules. [1]
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Notes