Chemistry - Module 3 Chemical Reactions Inquiry question: What are the products of a chemical reaction? 1.1.Investigate a variety of reactions to identify possible indicators of a chemical change Chemical change: New substances with different compositions and properties are formed Physical change: Changes in properties or state that don’t alter the composition Indicators of a chemical reaction: 1. Significant temperature change 2. Formation of a solid (precipitate) 3. Production of an odour 4. Production of a gas 5. Permanent change in colour 1.2 Use modelling to demonstrate 1.2.1 The rearrangement of atoms to form new substances - Chemical bonds can be broken or created - Each side is balanced number of atoms 1.2.2 The conservation of atoms in a chemical reaction Matter cannot be created nor destroyed - therefore mass of products = mass of reactants (in a different form) 1.3 Conduct investigations to predict and identify the products of a range of reactions, for example: Reaction Diagram Example Synthesis Decomposition (thermal, electrolysis, photolysis) Combustion (hydrocarbon) Incomplete - Not enough oxygen available - Not all of the carbon converts into carbon dioxide - Carbon monoxide and/or pure Carbon (soot) are produced 1
Transcript
Chemistry - Module 3
Chemical Reactions Inquiry question: What are the products of a chemical reaction?
1.1.Investigate a variety of reactions to identify possible indicators of a chemical change Chemical change: New substances with different compositions and properties are formed Physical change: Changes in properties or state that don’t alter the composition Indicators of a chemical reaction:
1. Significant temperature change 2. Formation of a solid (precipitate) 3. Production of an odour 4. Production of a gas 5. Permanent change in colour
1.2 Use modelling to demonstrate
1.2.1 The rearrangement of atoms to form new substances - Chemical bonds can be broken or created - Each side is balanced number of atoms
1.2.2 The conservation of atoms in a chemical reaction
Matter cannot be created nor destroyed - therefore mass of products = mass of reactants (in a different form)
1.3 Conduct investigations to predict and identify the products of a range of reactions, for example:
Reaction Diagram Example
Synthesis
Decomposition (thermal, electrolysis, photolysis)
Combustion (hydrocarbon)
Incomplete - Not enough oxygen available - Not all of the carbon converts into carbon dioxide - Carbon monoxide and/or pure Carbon (soot) are produced
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Complete - Excess oxygen - Only products are carbon dioxide and water
Precipitation
Insoluble salt (precipitate) when two solutions containing soluble salts are combined. Ions not involved in forming the precipitate are spectator ions
Easy way to remember, hydroxide is basic so use the acid/base equation
Acid/metal carbonates
Tests for gases
Gas Test Test result
Oxygen O2 Glowing splint Relights the splint
Hydrogen H2 Lit splint Pop sound
Carbon dioxide CO2 Limewater Turns it from clear and colourless to white and milky
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1.4 Investigate the chemical processes that occur when Aboriginal and Torres Strait Islander Peoples detoxify poisonous food items Cycad Why they must be detoxified
- Poisonous when ingested, symptoms arise of poisoning within 24 hours of being consumed
- Vomiting, Diarrhea, weakness, seizures, liver failure and hepatotoxicity How the Aboriginal people detoxified them
1. Leaching: The kernels are cut open and ground, then soaked in water. The toxins are soluble and washed out. The fruit can be then used to make bread
2. Fermentation: The kernels are stored for months in a warm moist environment which allows them to ferment. Following this they lose their toxicity.
Chemistry behind the process
- In leaching, the surface area is increased. The surface area to volume ratio allows the kernels to soak fully in stream of water, and the toxins are soluble, thus dissolving in the water.
- In fermentation, the toxins break down and carbon dioxide is produced 1.5 Construct balanced equations to represent chemical reactions Spectator ion/Net ionic equations Word equation: hydrochloric acid(aq) + calcium carbonate(aq)→calcium chloride(aq) + water(l)+ carbon dioxide(g)
Balanced equation: 2HCl(aq) + CaCO3 (aq) → CaCl2 (aq) + H20(l) + CO2 (g) Net ionic equation: 2H+
- Everything in aqueous form can be broken down into ions - Cross off the ions that are equal on each side of the equation, coloured in pink - Rewrite this equation, removing anything crossed off previously to make net ionic eqn
2H+(aq) + CO3 (aq) → + H20(l) + CO2 (g)
Spectator ions: Definition - set of ions that do not undergo chemical change Cl-(aq)
+ Ca+2(aq)
- These are the ions in pink, that are unchanged during the reaction
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Polyatomic ions: Common substances: Common metal ions:
- Silver: Ag + - Copper: Cu +2 - Iron: Fe +2 or Fe +3 - Zinc: Zn +2 - Lead: Pb +2
Some solubility rules:
Soluble: Insoluble:
Nitrates (NO3-) All n/a
Chlorides (Cl-) All Ag, Pb
Sulfates (SO4-2) All Ag, Pb, Ca, Ba...
Hydroxides (OH-) Ba, Ra... All
Carbonates (CO3-2) Na, K and NH4 All
Note: use the data sheet “solubility constants” everything on there is insoluble
Predicting Reactions of Metals Inquiry question: How is the reactivity of various metals predicted?
2.1 Conduct practical investigations to compare the reactivity of a variety of metals:
Metal Reaction with
Oxygen Water Dilute Acid Solution of metal ions
K
React with oxygen
(forms metal oxide)
Displace hydrogen with
cold water (forms metal hydroxide)
React with acids (HCl and H2SO4) (forms metal
ions and hydrogen gas)
Not tested Na
Li
Ca
Mg Displace hydrogen with
steam
Will displace the ion of a metal lower in the series from a solution of its salt Al
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Mn (forms metal oxide)
Zn
Cr
Fe
Co
No reaction in normal conditions
Ni
Sn
Pb
Cu
Ag No reaction No reaction
Au
2.2 Construct a metal activity series using the data obtained from practical investigations and compare this series with that obtained from standard secondary-sourced information A metal that is higher in the activity series will displace the ion of a less reactive metal from solution Don’t need to remember this, just look at the standard potentials on the data sheet
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2.3 Analyse patterns in metal activity on the periodic table and explain why they correlate with, for example:
Definition Down a Group
Across a Period (left → right)
Ionisation Energy Energy required to remove one electron from an atom
Decreases Increases
Atomic Radius Distance from the nucleus to the valence electrons
Increases Decreases
Electronegativity Ability of atoms to attract electrons
Decreases Increases
Core Charge Attractive force between the valence electrons and the
nucleus of the atom
No change Increases
Reactivity of Metals
Increases Decreases
2.4 Apply the definitions of oxidation and reduction in terms of electron transfer and oxidation numbers to a range of reduction and oxidation (redox) reactions Redox = reduction and oxidation Remember: OIL RIG
- Oxidation loses electrons - Electrons on the LHS of equation
- Reduction gains electrons - Electrons on the RHS of equation
- # of e- lost in oxidation = # of e- gained in reduction
Redox agents:
- Oxidising agent: oxidises the other substance and is being reduced itself - Reducing agent: reduces the other substance and is being oxidised itself
Oxidation number/state:
- Corresponds to the loss /gain of electrons - Loss of e = oxidised = increase in oxidation state - Gain of e = reduced = decrease in oxidation state
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Rules for calculating oxidation states: - Elemental form and neutral molecules: 0 - Monatomic ions: equal to their overall charge (including the sign)
- Eg. Cu+2 = 2 and S-2 = -2 - Polyatomic ions: equal to their overall charge (including the sign)
- Most electronegative usually has -ve OS - Eg. OH- = -1 and SO4
-2 = -2 - Note: the sum of the oxidation states of the atom = this number
2.5 Conduct investigations to measure and compare the reduction potential of galvanic half-cells Galvanic cell: Device that uses a chemical reaction (redox) to generate electricity. Electrode: conductors of a cell, connected to external circuit Anode: Electrode where oxidation occurs, electrons flow out here, net negative charge Cathode: Electrode where reduction occurs, electrons flow to here, net positive charge Electrolyte: aqueous/molten substance that conducts electricity
- Nitrates are used as they are soluble with all elements
Salt bridge: The path for ions to flow without mixing the contents of the half cells, completes the circuit Calculating reduction potentials (voltage):
- Find both agents on the standard potentials page - Whichever is higher up is oxidised, swap the sign on the relevant voltage (cause it
shows V for reduction) - Add the V value from the other agent (don’t change sign) to the the oxidised agent - Reaction will only occur if this value is positive - The agent reduced must have a higher reduction potential than the agent being oxidised
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Study of zinc cell and copper cell: - Zinc is oxidised because it is higher on the page,
therefore it is losing electrons and is the anode - Copper is oxidised because it is lower on the page,
therefore it is gaining electrons from zinc and forming cathode
- See the oxidising and reduction half equations → - Reduction potential / voltage:
- Zinc: - 0.76 V (change to +ve cause it is oxidised rather than reduced)
- Copper: 0.34 V (stays the same cause reduced)
- Add the two values together: 0.76 + 0.34 = 1.1V of energy passing in the circuit
2.6 Construct relevant half-equations and balanced overall equations to represent a range of redox reactions Creating half-equations from chemical equations
1. Calculate by looking charges at ions present 2. Use the standard reduction potentials (higher up = oxidised) 3. Checking change in oxidation state numbers (decrease=reduction, increase=oxidation)
In a balanced half- and overall equation
- Number of atoms of each element is equal on both sides (standard balancing) - Total charge on each side is equal (balancing electrons)
2.7 Predict the reaction of metals in solutions using the table of standard reduction potentials Understanding the standard reduction potentials
- Arranged in decreasing order of reactivity - Voltage readings are correct at:
- Concentration 1mol/L - SLC: 25ºC and 1atm
- Higher up = more likely to oxidise - Everything above:
- Hydrogen will react with acids - Water will react with water - Oxygen will react with oxygen
2.8 Predict the spontaneity of redox reactions using the value of cell potentials
- To get oxidation standard potential, swap the sign of the V - A reaction will occur when Eoxidation + Erediction = Etotal is positive
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Rates of Reactions Inquiry question: What affects the rate of a chemical reaction?
3.1 Conduct a practical investigation, using appropriate tools (including digital technologies), to collect data, analyse and report on how the rate of a chemical reaction can be affected by a range of factors, including but not limited to:
Increase in _____ Will cause_______ in rate of reaction
3.1.2 Temperature INCREASE
3.1.3 Surface area of reactant(s) INCREASE
3.1.4 Concentration of reactant(s) INCREASE
3.1.5 Catalysts INCREASE
Ways to measure the rate of a reaction:
- Volume of gas produced over a period of time (gas syringe) - Mass lost over a period of time (electronic balance) - Change in temperature over a period of time (thermometer) - Change in colour/turbidity over time (only for precipitations)
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3.2 Investigate the role of activation energy, collisions and molecular orientation in collision theory Requirements for collision / Collision theory
Collisions - Particles must make contact with each other for the reaction to occur
Activation energy
Definition: The minimum amount of energy required for a reaction to occur (break the bonds in the reactants)
- If energy is > Ea, the reaction will occur
- If not, particles will only bounce - Note Ea is different for every
reaction
Molecular orientation
- Must collide in the favourable orientation for reaction to occur
- Assuming there is enough energy for reaction to occur
- Correct orientation to both break
and form bonds
3.3 Explain a change in reaction rate using collision theory
- Larger number of successful collisions per minute = faster rate of reaction - Explain using terms “collision frequency” or “number of successful collisions per
minute” Energy distribution diagrams
- Particles to the right of the Ea line have sufficient energy for reaction to occur - Shaded green area
Standard
- Usually a bell curve - All particles possess some
energy - Most particles possess an
average amount of energy
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Temperature
Increasing temperature, increases kinetic energy and thus shifts the graph to the right
- More particles possess energy > activation energy
- ∴ more successful collisions - And faster rate of reaction
Concentration
Greater concentration by: - Increasing concentration of
reacting solutions - Increasing pressure of
reacting gases Note: increasing amount of solid reactants does not affect the rate of reaction
- More particles in same space therefore more collisions
Catalyst
- Lowers the activation energy Note a catalyst does nott:
- Get used up in the reaction - Affect the equilibrium
Surface area
Increase in surface area means more of the particle is exposed to the other reactant.
- More collisions will occur → increasing rate of reaction
