Reacting gas volume ratios of reactants or products (Avogadro's Law,
In the diagram above, if the
volume on the left syringe is twice that of the gas volume in the right, then
there are twice as many moles or actual molecules in the left-hand gas syringe.
Gay-Lussac's Law of volumes states that 'gases combine with each other in
simple proportions by volume'.
Law states that
'equal volumes of gases at the same temperature and pressure contain the same number of molecules'
or moles of gas.
This means the
of the equation or the relative moles of reactants and products
automatically gives us the gas volumes ratio
of reactants and products,
if all the gas volumes are measured at the same temperature and pressure.
calculations only apply to gaseous reactants or products AND if they are all at
the same temperature and pressure.
Given the equation: HCl(g)
+ NH3(g) ==> NH4Cl(s)
hydrogen chloride gas combines with 1 mole of ammonia gas to give 1 mole
of ammonium chloride solid.
1 volume of hydrogen chloride
will react with 1 volume of ammonia to form solid ammonium chloride
e.g. 25cm3 + 25cm3
==> solid product
or 400dm3 + 400 dm3 ==>
solid product (no
Given the equation: N2(g)
+ 3H2(g) ==> 2NH3(g)
1 mole of
nitrogen gas combines with 3 mols of hydrogen gas to form 2 mol of a
1 volume of nitrogen reacts with
3 volumes of hydrogen to produce 2 volumes of ammonia
e.g. 50 cm3 nitrogen
reacts with 150 cm3 hydrogen (3 x 50) ==> 100 cm3 of
ammonia (2 x 50)
10.3: Given the equation: C3H8(g) + 5O2(g)
==> 3CO2(g) + 4H2O(l)
1 mole of propane gas reacts with
5 mols of oxygen gas to form 3 moles of carbon dioxide gas and 4 mols of
(a) What volume of oxygen
is required to burn 25cm3 of propane, C3H8.
volume ratio is C3H8 : O2 is 1 : 5
for burning the fuel propane.
so actual ratio is 25
: 5x25, so 125cm3 oxygen is needed.
(b) What volume of carbon
dioxide is formed if 5dm3 of propane is burned?
reactant-product volume ratio is C3H8 : CO2
is 1 : 3
so actual ratio is 5
: 3x5, so 15dm3 carbon dioxide is formed.
(c) What volume of air (1/5th
oxygen) is required to burn propane at the rate of 2dm3 per minute
in a gas fire?
volume ratio is C3H8 : O2 is 1 : 5
so actual ratio is 2
: 5x2, so 10dm3 oxygen per minute is needed,
therefore, since air is
only 1/5th O2, 5 x 10 = 50dm3
of air per minute is required
Example 10.4: Given
the equation: 2H2(g) + O2(g) ==> 2H2O(l)
Example 10.5: It was
found that exactly 10 cm3 of bromine vapour (Br2(g))
combined with exactly 30 cm3 chlorine gas (Cl2(g))
to form bromine-chlorine compound BrClx.
a) From the reacting gas volume ratio,
what must be the value of x? and hence write the formula of the compound.
b) Write a balanced equation to
show the formation of BrClx
The reacting gas volume ratio is
1 : 3, therefore we can write with certainty that 1 mole (or molecule) of
bromine reacts with 3 moles (or molecules) of chlorine, and balancing the
symbol equation, results in two moles (or molecules) of the bromine-chlorine
compound being formed.
[rgv] type in answer
OTHER CALCULATION PAGES
What is relative atomic mass?,
relative isotopic mass and calculating relative atomic mass
formula/molecular mass of a compound or element molecule
Law of Conservation of Mass and simple reacting mass calculations
Composition by percentage mass of elements
in a compound
Empirical formula and formula mass of a compound from reacting masses
(easy start, not using moles)
Reacting mass ratio calculations of reactants and products
moles) and brief mention of actual percent % yield and theoretical yield,
and formula mass determination
Introducing moles: The connection between moles, mass and formula mass - the basis of reacting mole ratio calculations
(relating reacting masses and formula
moles to calculate empirical formula and deduce molecular formula of a compound/molecule
(starting with reacting masses or % composition)
Moles and the molar volume of a gas, Avogadro's Law
Reacting gas volume
ratios, Avogadro's Law
and Gay-Lussac's Law
Molarity, volumes and solution
concentrations (and diagrams of apparatus)
do volumetric titration calculations e.g. acid-alkali titrations
(and diagrams of apparatus)
Electrolysis products calculations (negative cathode and positive anode products)
e.g. % purity, % percentage & theoretical yield, volumetric titration
apparatus, dilution of solutions
(and diagrams of apparatus), water of crystallisation, quantity of reactants
required, atom economy
Energy transfers in physical/chemical changes,
Gas calculations involving PVT relationships,
Boyle's and Charles Laws
Radioactivity & half-life calculations including
Revision KS4 Science Additional
Science Triple Award Science Separate Sciences Courses aid to textbook revision
GCSE/IGCSE/O level Chemistry Information Study Notes for revising for AQA GCSE
Science, Edexcel GCSE Science/IGCSE Chemistry & OCR 21st Century Science, OCR Gateway
Science WJEC gcse science chemistry CCEA/CEA gcse science chemistry O
Level Chemistry (revise courses equal to US grade 8, grade 9 grade 10) A level
Revision notes for GCE Advanced Subsidiary Level AS Advanced Level A2 IB Revise
AQA GCE Chemistry OCR GCE Chemistry Edexcel GCE Chemistry Salters Chemistry CIE
Chemistry, WJEC GCE AS A2 Chemistry, CCEA/CEA GCE AS A2 Chemistry revising
courses for pre-university students (equal to US grade 11 and grade 12 and AP
Honours/honors level for revising science chemistry courses revision guides
content copyright © Dr W P Brown 2000-2011 All rights reserved
revision notes, puzzles, quizzes, worksheets, x-words etc. * Copying of website
material is not permitted
Alphabetical Index for Science
B C D
G H I J K L M
N O P
U V W
X Y Z