Chemical Reactions BIOB111 CHEMISTRY & BIOCHEMISTRY Session 3
Chemical Reactions
BIOB111
CHEMISTRY & BIOCHEMISTRY
Session 3
Key concepts: session 3From this session you are expected to develop an understanding of the following concepts:
Concept 1: Chemical reactions
Concept 2: Bond breakage/formation in chemical reactions
Concept 3: Interpreting chemical reactions: coefficients and subscripts
Concept 4: Redox reactions
Concept 5: Avogadro’s number
Concept 6: Usefulness of the mole
Concept 7: Using the mole unit
These concepts are covered in the Conceptual multiple choice questions of tutorial 3
Session OverviewPart 1: Chemical equations
• Chemical vs Physical change
• Chemical equations represent chemical reactions
• Balancing chemical equations
Part 2: Redox reactions
• Redox reactions
Part 3: The mole
• What is the mole?
• Using the mole
Part 1: Chemical equations
• Chemical vs Physical change
• Chemical equations represent chemical reactions
• Balancing chemical equations
• Physical change:– Matter can be changed from one state to another e.g. from solid into liquid
– Hallmarks of physical change:
• No new substances are created
• The type of matter present before the physical change is the same as the matter present after physical change
Changing the state of water via physical
change
Chemical vs Physical change
• Chemical change:– Matter can be changed from one substance into another
substance via a chemical reaction
– Hallmarks of chemical change:• One or more new substances are created
– The molecular structure of the original substance(s) changes in the chemical reaction forming one or more new substances
• The type of matter present before the chemical change is different from the matter present after the chemical change
Changing original substance(s) (reactants) to
different substance(s) (products) via chemical
change
Chemical reaction:
Chemical vs Physical change
Chemical equations represent chemical reactions
• In a chemical reaction, 1 or more original substances (REACTANTS) are converted to 1 or more new substances (PRODUCTS)
• A chemical reaction is usually written in a chemical equation
Chemical reaction:
Reactant 1 Reactant 2 Product 1Product 2
Chemical equation: Is a diagram of a chemical reaction
– Reactants are shown on the left & products on the right
– The arrow shows the progress of the chemical reaction
Progression through a chemical reaction:
– Start- step 1: The chemical bonds holding the reactants together are broken• Chemical bond breakage requires an energy input
• Example below: Chemical bonds broken within methane and oxygen
– Middle- step 2: Once the chemical bonds have been broken, the atoms rearrange to adopt new positions
• Example below: Carbon, hydrogen and oxygen atoms rearrange
– End- step 3: After atom rearrangement, new chemical bonds form between the atoms creating the products
• Chemical bond formation releases energy
Example below: New chemical bonds are formed to produce carbon dioxide and water
Chemical equations represent chemical reactions
Chemical reaction:
Reactant 1 Reactant 2 Product 1Product 2
+ +H
H
HH
H H
H H
C C
OO
O OO O
O
O
Reactant 1:Methane Reactant 2:
Oxygen Product 1:Carbon dioxide
Product 2: water
Chemical equations represent chemical reactions
Start- step 1:
Chemical bond breakage in reactants
+H
H
HH C
OO
O O
Reactant 1:Methane Reactant 2:
Oxygen
Covalent bond broken• Bond
breakage requires energy
Chemical equations represent chemical reactions
Middle- step 2:
Atom rearrangement
+H
H
HH C
OO
O O
Chemical equations represent chemical reactions
End- step 3:
Chemical bond formation in products
C
O O
H H
O
Product 1:Carbon dioxide
Product 2: Water
H
O
H
Newly formed covalent bond• Bond formation
releases energy Product 2: Water
Chemical equations represent chemical reactions
+ +H
H
HH
H H
H H
C C
O O
O
O
HC 1 41 22 O 21 OC 1 H 22 O 1
Reactant 1:Methane Reactant 2:
Oxygen Product 1: Carbon Dioxide
Product 2:Water
OO
O O
Chemical equations represent chemical reactions
1(CH4) 2(O2)+ 1(CO2) 2(H2O)+CH4 2O2+ 2H2OCO2 + Simplified
representation
Chemical equations represent chemical reactions
Law of conservation of matter:
Atoms can neither be created nor destroyed, only rearranged
• According to the law of conservation of matter
for chemical reactions:– The number and type of atoms present in the reactants (left of the arrow) must equal
the number and type of atoms in the products (right of the arrow)• The chemical reaction must be balanced
– The conversion of reactants to products during a chemical reaction relies on atom rearrangement
• No new atoms are created in a chemical reaction
• No atoms are destroyed in a chemical reaction
CH4 2O2+ 2H2OCO2 +
Chemical equations represent chemical reactions
The chemical formula of a molecule shows the number of
each type of atom present in the molecule
In 1 molecule of H2O:
1(H2O)
×
×
• 1 × H2 = 2 hydrogen atoms (in 1 molecule of H2O)
In 3 molecules of H2O:
3(H2O)
×
×
• 3 × H2 = 6 hydrogen atoms (in 3 molecules of H2O)
H H
O
• 1 × O = 1 oxygen atoms (in 1 molecule of H2O)
• 3 × O = 3 oxygen atoms (in 3 molecules of H2O)
Chemical equations represent chemical reactions
Number of hydrogen atoms in 1 molecule of H2O:
Number of oxygen atoms in 1 molecule of H2O:
Number of hydrogen atoms in 3 molecules of H2O:
Number of oxygen atoms in 3 molecules of H2O:
Subscript– The subscript identifies the number atoms of a specific element present in a molecule
• The subscript only affects the atom type that the subscript number comes after
– Example: the subscript of 4 within CH4 establishes that there are 4 hydrogen
atoms in the CH4 molecule
CH4 2O2+ 2H2OCO2 +Chemical equations represent chemical reactions
– Subscripts cannot be changed in a chemical reaction
• If the subscript was changed, it would no longer be the same molecule
– If the subscript is 1, it is not shown• In theory, CH4 could be written as C1H4 ,
as there is one carbon atom in the CH4 molecule
CH4 2O2+ 2H2OCO2 +Coefficient– The coefficient identifies the number molecules present in the chemical equation
– The coefficient is always written in front of the formula• The coefficient can be changed when attempting to balance the equation
– Example: The coefficient of 2 in front of H2O means there is two separate H2O molecules on the product side of the equation
Chemical equations represent chemical reactions
– The coefficient is always a whole number
– A coefficient of 1 is not normally shown
• In theory, CH4 could be written as 1CH4 , as there is one molecule of CH4 in the chemical
equation
Activity: Identify the coefficients and subscripts
in the chemical equation below
Why is the chemical equation on the left (blue) correct,
whereas the chemical equation on the right (red) is incorrect?
H2 + O2 → H2O 2H2 + O2 → 2H2O
Chemical equation is unbalanced
There are different numbers of one or
more atom types on the reactant and
product side of the chemical equation
Chemical equation is balanced
There are the same number of each atom
type on the reactant and product side of
the chemical equation
Chemical equations represent chemical reactions
Method for balancing a chemical equation
Step 1: Determine if the chemical equation is balanced
Step 2: Balance the chemical equation by changing one or
more coefficients in front of the molecules
Step 3: Check whether adjustments to the coefficients have
balanced the chemical equation
Balancing chemical equations
Balancing chemical equations• To work out the number of an elements’ atoms present in a molecule
multiply the coefficient by the subscript
– For 2Fe2O3
Coefficient
SubscriptThe number of Fe atoms:
Coefficient is 2 and subscript is 2:
2 × 2 = 4 Fe atoms
• The chemical equation must have the lowest possible
coefficients
– E.g. 4Fe + 3O2 → 2Fe2O3 is correct
8Fe + 6O2 → 4Fe2O3 is incorrect
The number of O atoms:
Coefficient is 2 and subscript is 3:
3 × 2 = 6 O atoms
Method for balancing a chemical equation
Step 1: Determine if the equation is balanced
• List the element types present on the reactant side and the product side of the
equation
– Count the number of each type of element present on each side of the equation
Fe + O2 → Fe2O3
Balancing chemical equations
Reactant atomtypes
Number of reactant atoms
Product atom types
Number of product atoms
Different numbers of Fe and O atoms
on the reactant and product side of the
equation = Unbalanced
equation
Fe (iron)
O (oxygen)
1
2
2
3
Fe (iron)
O (oxygen)
Method for balancing a chemical equation
Step 2: Balance the chemical equation by changing one or
more coefficients in front of the molecules
Balancing chemical equations
Fe + O2 → Fe2O3
• Try changing one or more of the coefficients to balance the chemical equation
– Often trail and error is needed to get the correct answer
• Once coefficients have been changed, move to step 3 to check if the equation is balanced
4Fe + 3O2 → 2Fe2O3
Method for balancing a chemical equation
Step 3: Check whether adjustments to the coefficients have balanced
the chemical equation
• List the element types present on the reactant side and the product side of the equation– Count the number of each type of element present on each side of the equation
– Essentially, a repeat of step 1
• If the chemical equation is not balanced repeat step 2 (try a different combination of coefficients)
Balancing chemical equations
4Fe + 3O2 → 2Fe2O3
Reactant atomtypes
Number of reactant atoms
Product atom types
Number of product atoms
The numbers of Fe and O atoms on the
reactant and product side of the equation are equal
= Balanced equation
Fe (iron)
O (oxygen)
4
6
4
6
Fe (iron)
O (oxygen)
Balancing the chemical equation below:
Na + N2 → Na3N
NNa N Na Na
Na
N
More sodium atoms are needed on the reactant side
Balancing chemical equations
Balancing chemical equations
Balancing the chemical equation below:
3Na + N2 → Na3N
N
Na
N Na Na
Na
N
More nitrogen atoms are needed on the product side
Na
Na
Balancing chemical equations
Balancing the chemical equation below:
3Na + N2 → 2Na3N
N
Na
N Na Na
Na
N
More sodium atoms are needed on the reactant side
Na
Na
Na Na
Na
N
Balancing chemical equations
Balance the following chemical equation:
6Na + N2 → 2Na3N
N
Na
N Na Na
Na
NNa
Na
Na Na
Na
N
Na
Na
NaSame number of sodium and nitrogen atoms present on the reactant and product side of the equation = balanced equation
Balancing chemical equations
Balanced chemical equation:
6Na + N2 → 2Na3N
N
Na
N Na Na
Na
NNa
Na
Na Na
Na
N
Na
Na
NaReactant atom
typesNumber of
reactant atomsProduct atom
typesNumber of
product atoms
Na (sodium) 6 Na (sodium) 6
N (nitrogen) 2 N (nitrogen) 2
Is the chemical reaction
below balanced?
Reactant atomtypes
Number of reactant atoms
Product atom types
Number of product atoms
2Al + Fe2O3 → 2Fe + Al2O3
Balance the chemical equation below:
H2 + O2 → H2O
Reactant atomtypes
Number of reactant atoms
Product atom types
Number of product atoms
Balance the chemical equations by
choosing the correct coefficient sets
Which set of coefficients balances the
equation?
N2 + H2 NH3
a) 2, 1, 3
b) 1, 3, 2
c) 1, 2, 3
Which set of coefficients balances the
equation?
__Mg + _N2 → __Mg3N2
a) 1, 3, 2
b) 3, 1, 2
c) 3, 1, 1
Describe what happens during a chemical reaction
by referring to the reactants and products.
How do atom rearrangements help facilitate
chemical reactions?
Is it possible for the products of a chemical reaction
to be converted back into the original reactants?
Why/why not?
Key concept: chemical reactions
Attempt Socrative questions: 1 to 4
Google Socrative and go to the student login
Room name:
City name followed by 1 or 2 (e.g. PERTH1)
1 for 1st session of the week and 2 for 2nd session of the week
Summary Part 1: Chemical equations
• Chemical vs Physical change– Chemical change occurs during a chemical reaction
• The type of matter present before the chemical change is different from the matter present after the chemical change
– Physical change involves a substance changing its physical state,
such as a solid being converted to a liquid• No new substances are created as a result of physical change
• No chemical reactions occur during a physical change
• Chemical equations represent chemical reactions– In a chemical reaction, the reactants on the left hand side are converted
into the products on the right hand side of the equation, with the arrow representing the progression of the chemical reaction
• CH4 + 2O2 → CO2 + 2H2O
– No atoms are created or destroyed in a chemical reaction, only rearranged to form new substances (products)
Summary Part 1: Chemical equations
• Balancing chemical equations
– The same number of each type of atom must be present on both the reactant and product side of the chemical equation
• No atoms are created or destroyed in a chemical reaction, only rearranged to form new substances (products)
– To assess whether a chemical equation is balanced count the number of each type of atom on the reactant and product side
• If the number of each type of atom are equal on both sides, the chemical equation is balanced
• If the number of one or more types of atom are different on the reactant and product sides of the chemical equation, the chemical equation is unbalanced
– The coefficients in front of the molecules (reactants and products) in the chemical equation can be changed to balance the equation
Part 2: Redox reactions
• Redox reactions
Redox reactions
Combustion reactions are the most common type of chemical reaction
– Combustion reactions always involve a substance reacting with oxygen
– When organic hydrocarbons like methane (CH4) combust:
• Water, carbon dioxide and energy (light and heat) are produced
– All combustion reactions are
redox reactionshttp://www.chem.ucla.edu/harding/IGOC/C/combustion.html
https://www.freeimages.com/photo/fire-1495233
CH4 + 2O2 → CO2 + 2H2O + energy
Electrons H atoms O atoms
OXIDATION Loss of electrons Loss of H atoms Gain of O atoms
REDUCTION Gain of electrons Gain of H atoms Loss of O atoms
OXIDATION: Loss of 1 or more hydrogen atoms
REDUCTION: Gain of 1 or more hydrogen atoms
H1p+
1e-
Redox reactions
• Oxidation and reduction are complementary processes– Oxidation and reduction occur simultaneously because the compound that
loses hydrogen (oxidation) donates it to another compound which accepts the hydrogen (reduction)
• Losing or gaining hydrogen atoms is equivalent to losing or gaining electrons – Each hydrogen atom contains 1 electron (and 1 proton)
• In a redox reaction, electrons and/or hydrogen atoms are transferred from one compound to another
OIL RIG useful to remember what happens in a redox reaction:
Oxidation Is Loss of electrons and/or hydrogen atoms (OIL)
Reduction Is Gain of electrons and/or hydrogen atoms (RIG)
Redox reactions
Redox reactions
• In a redox reaction, one reactant is oxidised and one is reduced
• To determine which reactant is oxidised and which is reduced:– Assess how each reactant changes during the chemical reaction by looking at
the products
• The reactant that has lost hydrogen to become the product has been oxidised
• The reactant that has gained hydrogen to become the product has been reduced
CH4 2O2+ 2H2OCO2 +CH4 loses hydrogen = oxidised
O2 gains hydrogen = reduced
Redox reactions
• In a redox reaction, one reactant is oxidised and one is
reduced
Biological molecule loses 2 hydrogens = oxidised
Coenzyme gains 2 hydrogens = reduced
Adapted from Timberlake 2013, p223-224
• Redox reaction are vital to many
metabolic pathways required to
generate cellular energy (ATP)
including:
– Glycolysis
– Citric acid cycle
– The electron transport chain
• The coenzymes that are commonly
used in redox reactions (within
metabolic pathways) can exist in either:– An electron/hydrogen rich form
– An electron/hydrogen poor form
Electron poor coenzymes
Electron rich coenzymes
NAD+ NADH
NADP NADPH
FAD FADH2
Adapted from Timberlake 2013, p223-224
Redox reactions
Identify which reactant is oxidised and which is
reduced in the chemical reaction below
2NH3 + 3O2 → N2 + 6H2O
• NH3 loses hydrogen to become N2, hence NH3 is oxidised– Oxidation is loss of hydrogen/electrons
• O2 gains hydrogen to become H2O, hence O2 is reduced– Reduction is gain of hydrogen/electrons
• Oxygen is always reduced in redox reactions
NH3 loses hydrogen = oxidised
O2 gains hydrogen = reduced
Malate-H + NAD+ → Oxaloacetate + NADH
• Malate-H loses hydrogen to become oxaloacetate, hence
Malate-H is oxidised
– Oxidation is loss of hydrogen/electrons
• NAD+ gains hydrogen to become NADH, hence NAD+ is reduced
– Reduction is gain of hydrogen/electrons
Identify which reactant is oxidised and which is
reduced in the chemical reaction below
Malate-H loses hydrogen = oxidised
NAD+ gains hydrogen = reduced
When a molecule loses hydrogen atoms in a chemical
reaction, is the molecule oxidised or reduced?
What about if the molecule gains a hydrogen atoms?
In the above reaction, which molecule is oxidised?
How does the oxidised molecule
change during the redox reaction?
In the above reaction, which molecule is reduced?
How does the reduced molecule
change during the redox reaction?
Key concept: redox reactions
CH4 + 2O2 CO2 + 2H2O
Attempt Socrative questions: 5 and 6
Google Socrative and go to the student login
Room name:
City name followed by 1 or 2 (e.g. PERTH1)
1 for 1st session of the week and 2 for 2nd session of the week
Part 2: Redox reactions
• Redox reactions
– A redox reaction involves one reactant being oxidised and one
reactant being reduced
• Oxidation and reduction occur simultaneously in a redox reaction
– Oxidation is the loss of electrons/hydrogen atoms
– Reduction is the gain of electrons/hydrogen atoms
– OIL RIG: Oxidation Is Loss, Reduction Is Gain
– The reactant that has loses hydrogen to become the product
has been oxidised
– The reactant that has gains hydrogen to become the product
has been reduced
Part 3: The mole
• What is the mole?
• Using the mole
• Amount of a substance is specified by numbers or collection terms:
– 1 dozen eggs
= 12 eggs
– 1 slab of beer
= 24 cans
– 1 mole of hydrogen atoms
= 6.02 × 1023 hydrogen atoms
What is the mole?
https://www.freeimages.com/photo/eggs-1194166
How was the mole determined?
The mole unit is relative to the amount of atoms in 12 grams of carbon-12 atoms
– 1 gram of Carbon-12 atoms:• Contains 6.02 x 1023 carbon 12 atoms
• Weighs 12.01 grams
– 1 mole of any component
= 6.02 x 1023 components of that thing
• 1 mole of Na = 6.02 x 1023 Na atoms
• 1 mole of H2O = 6.02 x 1023 H2O molecules
• 1 mole of CO2 = 6.02 x 1023 CO2 compounds
• 1 mole = 6.02 x 1023 components of that substance– 6.02 x 1023 = Avogadro’s number
Putting the mole into perspective
• One mole of hydrogen atoms is:– 6,020,000,000,000,000,000,000,000 hydrogen atoms
– Equal to 6.02 × 1023 hydrogen atoms (scientific notation)
• One mole of red blood cells
= the number of red blood cells
in every human on earth
• In a 1 litre bottle of water there are about
55.5 mole of H2O molecules
https://www.freeimages.com/photo/the-element-of-life-1364414
https://www.freeimages.com/photo/flowing-blood-1197512
What is the mole?
MOLE
How many individual components are in
one mole?
6.02 × 1023
COMPONENTS
1 MOLE OF HYDROGEN ATOMS =
6.02 × 1023
INDIVIDUAL HYDROGEN ATOMS
COUNTING VERY LARGE NUMBERS OF COMPONENTS E.G. ATOMS MOLECULES OR COMPOUNDS
ON A SIMPLE SCALE
Example
Useful for
Example
2 MOLE OF HYDROGEN ATOMS = 2 TIMES (6.02 × 1023)
INDIVIDUAL HYDROGEN ATOMS
What is the mole?
Number of components in one mole
is called AVOGADRO’S NUMBER
Using the moleWhat makes the mole useful?
• The mole can be used to quantify the amount of atoms,
molecules, or compounds in a sample on a useable scale
0 mole 1 mole 2 mole 3 mole 4 mole
Quantifying the number of
H2O molecules
6.02 × 1023
molecules1.20 × 1024
molecules
1.81 × 1024
molecules2.41 × 1025
molecules0
molecules
Example:
How many H2O molecules are in a 37 mL of water?
– 2.0 mole of H2O molecules = 1.20 × 1024 individual H2O molecules
• Much easier to count the number of H2O molecules in mole rather than
counting each individual H2O molecule
The chemical formula of a molecule shows the number of
each type of atom present in the molecule
In 1 molecule of H2O:
1(H2O)
×
×
• 1 × H2 = 2 hydrogen atoms (in 1 molecule of H2O)
In 3 molecules of H2O:
3(H2O)
×
×
• 3 × H2 = 6 hydrogen atoms (in 3 molecules of H2O)
H H
O
• 1 × O = 1 oxygen atoms (in 1 molecule of H2O)
• 3 × O = 3 oxygen atoms (in 3 molecules of H2O)
Chemical equations represent chemical reactions
Number of hydrogen atoms in 1 molecule of H2O:
Number of oxygen atoms in 1 molecule of H2O:
Number of hydrogen atoms in 3 molecules of H2O:
Number of oxygen atoms in 3 molecules of H2O:
Using the mole
1 mole of molecules of H2O = 6.02 × 1023
molecules of H2O
× 1 mole
In 1 mole of H2O, how many mole of hydrogen atoms and oxygen atoms are there?
The chemical formula of a molecule (e.g. H2O) specifies the number of moles of atoms
of each element present in one mole of that molecule (e.g. H2O)
In 1 mole of H2O molecules:
1 mole (H2O)×
×
• 1 mole × H2 = 2 mole of hydrogen atoms (in 1 mole of H2O)
In 3 moles of H2O molecules:
3 mole (H2O) • 3 mole × H2 = 6 mole of hydrogen atoms (in 3 moles of H2O)
×
×
3 mole of molecules of H2O = 3 lots of
6.02 × 1023
molecules of H2O
× 1 mole
× 1 mole
× 1 mole
• 1 mole × O = 1 mole of oxygen atoms (in 1 mole of H2O)
• 3 mole × O = 3 mole of oxygen atoms (in 3 moles of H2O)
Number of hydrogen atoms in 1 mole of H2O:
Number of oxygen atoms in 1 mole of H2O:
Number of hydrogen atoms in 3 mole of H2O:
Number of oxygen atoms in 3 mole of H2O:
Attempt Socrative questions: 7 to 10
Google Socrative and go to the student login
Room name:
City name followed by 1 or 2 (e.g. PERTH1)
1 for 1st session of the week and 2 for 2nd session of the week
Part 3: The mole
• What is the mole?– The mole is a way of counting very large number of any component
e.g. the number of atoms, molecules or compounds in a sample
– The number of components in 1 mole of a substance is 6.02 × 1023
• 6.02 × 1023 is Avogadro’s number
• Using the mole– The mole can be used to quantify the amount of atoms, molecules, or
compounds in a sample on a useable scale• E.g. 1.20 × 1024 hydrogen atoms = 2 moles of hydrogen atoms
• The chemical formula of a molecule (e.g. H2O) tells you the number of moles of atoms of each element present in one mole of that molecule (e.g. H2O)
• E.g. 1 mole of H2O molecules contains:– 2 moles of hydrogen atoms (1 mole × H2)
– 1 mole of oxygen atoms (1 mole × O)
Readings & Resources• Stoker, HS 2014, General, Organic and Biological Chemistry, 7th edn,
Brooks/Cole, Cengage Learning, Belmont, CA.
• Stoker, HS 2004, General, Organic and Biological Chemistry, 3rd edn, Houghton Mifflin, Boston, MA.
• Timberlake, KC 2013, General, organic, and biological chemistry: structures of life, 4th edn, Pearson, Boston, MA.
• Alberts, B, Johnson, A, Lewis, J, Raff, M, Roberts, K & Walter P 2008, Molecular biology of the cell, 5th edn, Garland Science, New York.
• Berg, JM, Tymoczko, JL & Stryer, L 2012, Biochemistry, 7th edn, W.H. Freeman, New York.
• Dominiczak, MH 2007, Flesh and bones of metabolism, Elsevier Mosby, Edinburgh.
• Tortora, GJ & Derrickson, B 2014, Principles of Anatomy and Physiology, 14th edn, John Wiley & Sons, Hoboken, NJ.
• Tortora, GJ & Grabowski, SR 2003, Principles of Anatomy and Physiology, 10th edn, John Wiley & Sons, New York, NY.
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