Module 3 Yr 11 Flashcards
Difference between physical and chemical change
Physical change: doesn’t result in the formation of new substances
Chemical change: involves the formation of new substances
Cause of chemical change
A reaction has occurred with chemicals bonds being broken and formed
Indicators of chemical change
Production of bubbles:
This might indicate that a gas (a new product) has been formed. However, production of bubbles can be also due to boiling of the reaction mixture in a hot reaction or vigorous movement of chemicals
Production of odour:
Indicates that a gas (a new product) has been formed
Change in temperature
This is due to the absorption or release of heat (endothermic or exothermic reaction)
Changes in temperature occur due to changes in bond energies upon the making and breaking of bonds
Formation of a precipitate
A precipitate is an insoluble solid formed when two clear solutions containing certain ions are reacted together.
Change in colour
This might indicate that a new product has been formed. However, a change in colour doesn’t always mean a chemical change has occurred. For example. the mixing of two paint colours to create a new colour is a physical process
Limitations and advantages of Bohr’s model
Limitations
It could only be applied to atoms with one valence electron
It didn’t explain the different intensities of lines/colours in a hydrogen spectrum
It didn’t explain the Zeeman effect
Advantages
Electrons are particles that occupy fixed orbits around the nucleus - called stationary orbits
Each orbit has an energy level associated with it
Energy is absorbed when an electron jumps from a lower orbit to a higher one and energy is emitted when an electron falls from a higher to a lower orbit
The energy and frequency of light emitted can be calculated using the difference between the two orbital energy levels
Limitations and advantages of Schrodinger’s model
Advantages
predicts the probability of an electron being at a certain location around the atom instead of defining a set radius
Schrodinger’s model allowed the electron to occupy three-dimensional space.
Limitations
This model no longer tells us where the electron is; it only tells us where it might be.
The disadvantage is that it is difficult to imagine a physical model of electrons as waves
Advantages and disadvantages of molecular modelling kits
Advantages:
Give a visual representation of bond formation and breaking
Are able to demonstrate different types of bonds such as double and triple bonds
Allows us to visualise how the conservation of mass is satisfied in chemical processes.
Disadvantages:
Doesn’t show electron transfer
Doesn’t demonstrate different strengths of bonds
Doesn’t account well for chemical reactions with ionic reagents/products
Do not show cause of bonds formation
Difference between complete ionic and net ionic equation
A net ionic equations cancels off the ions in the reactants and products whilst a complete ionic equation doesn’t cancel out the ions
General rules of synthesis
Two non-metals tend to produce a covalent compound
A metal and non-metal tend to produce an ionic compound
Two metals don’t chemically react together and instead combine physically to form alloys such as bronze from copper and tin and brass from copper and zinc
Define direct combination reaction
Two elements combine to form a compound
What is a decomposition reaction
one reactant is broken down into two or more constituent substances
What is electrolysis
What is photodecomposition/photolysis
An electric current is passed through a compound to induce a chemical reaction
Silver halide –> silver solid + halogen catalyst is UV light
A silver halide salt darkens under the action of UV light as silver solid is formed.
2AgCl (s) –> 2 Ag (s) + Cl2 (g)
What are organic fuels
Chemicals composed of C and H atoms and sometimes O atoms such as C8H15
Types of combustion reactions
Complete combustion occurs when there is sufficient oxygen supply
Fuel + oxygen –> carbon dioxide (g) + water (l)
Carbon in fuel becomes carbon dioxide due to sufficient oxygen supply
Produces high amounts of energy
Incomplete combustion occurs when there is insufficient oxygen supply
Fuel + oxygen –> carbon dioxide + carbon monoxide + carbon (s) + water
carbon as solid is soot (blackish powder)
Produces less energy due to less bonds being formed. Since energy is released in bond formation, incomplete combustion will not liberate as much energy as complete combustion.
Coefficient of oxygen can be a non-integer
Note: metal + oxygen –> isn’t combustion if heat isn’t involved, can be synthesis reaction
When are substances soluble
Soluble substance is one which >10g of solute can be dissolved per litre of solvent
Partially soluble substance is one which 1-10g of solute can be dissolved per litre of solvent
An insoluble substance is one which <1g can be dissolved per litre of solvent.
What compounds are soluble
Group I metal compounds
Ammonium compounds
Nitrate compounds
Acetate (ethanoate) compounds
Group 17
Sulfate compounds
What compounds are insoluble
Sulfates with PMS and Strong Calcium Bones
Group 17 with Strong Calcium Bones
Strong calcium bones: strontium, calcium and barium
PMS: Lead, Mercury and Silver
Difference between acid and base
State neutralisation reaction
Properties of acid vs base
Acids release H+ (aq) in aqueous solutions whilst bases release OH-(aq).
Acid + base –> salt + water
Acid: sour, corrosive, turn blue litmus red, conducts electricity
Base: bitter, caustic, turns red litmus red, conduct electricity
What is an acid + carbonate reaction
Type of neutralisation reaction
Acid + metal carbonate –> salt + water + carbon dioxide
Presence of carbon dioxide can be detected with limewater test
How is cycad detoxified
A type of palm that grows in Northern and North-Eastern Australia that bears poisonous fruit. It is detoxified by:
cutting and placing the fruit in mesh bags. They are soaked in water and over a few days, the toxins leach out.
Heat the fruit first resulting in thermal decomposition of toxin. It is then placed in a mesh bag and left in running stream water to leach out the toxins
Immerse the fruit in a closed pit of water. Enzymes in the water cause fermentation to occur resulting in the breakdown of toxins. This process, takes place over weeks to months.
Why are metal strips sanded before put in water
To remove outer oxide layer which is often unreactive. In certain metals (Mg, Al, Zn) this oxide layer forms on outer surface when exposed to air. Will passivate metal and render it inert to further reaction. Rust also coats metal which renders it unreactive
Metal and water reactions
Metal + water (l) –> metal hydroxide + hydrogen gas
Metal + steam –> metal oxide + hydrogen gas
Metal and dilute acid reaction
Metal + dilute acid –> salt + hydrogen gas
Displacement reaction
The more reactive metal displaces the less active metal in solution. If metal 1 is more reactive than metal 2.
Metal 1 solid + Metal 2 ions –> metal 1 ions + metal 2 solid
State metal activity series
key natural list but management after Zone fish country next service pattern could art positive audience
K>Na>Li>Ba>Ca>Mg>Al>Zn>Fe>Co>Ni>Sn>Pb>Cu>Ag>Pt>Au
States metal activity series reaction with oxygen
Reacts rapidly with oxygen: K, Na, Li, Ba, Ca
Reacts vigorously with oxygen: Mg, Al, Zn, Fe
Reacts slowly: Sn, Pb, Cu
Doesn’t react: Ag, Pt, Au
States metal activity series reaction with water
Reacts explosively with water: K, Na, Li, Ba
Reacts with cold water: Ca
Reacts with steam: Mg, Al, Zn, Fe
Doesn’t react: Sn, Pb, Cu, Ag, Pt, Au
States metal activity series reaction with dilute acid
High reactivity with dilute acid: K, Na, Li, Ba, Ca, Mg, Al, Zn, Fe
Reacts slowly: Sn, Pb
Will only react with hot and very concentrated acids: Cu, Ag, Pt, Au
Why does magnesium react with steam but not water
Steam contains more kinetic energy than liquid water. This will result in more frequency and more powerful collisions with metal surfaces than water (collision theory).
Less reactive metals such as Mg may require additional energy in order to react
What are the oxidation number/state for:
1. Molecules with one element or for neutral atoms
2. Molecules/compounds
3. Ions or polyatomic ions
4. Fluorine
5. Hydrogen in covalent compounds
6. Hydrogen in metal hydrides
7. Oxygen in compounds
- 0
- Addition of individual atomic oxidation states and sum up to 0. For example, the sum of oxidation states in Fe2O3 is 0, with each O having an oxidation state of -2 and thus the Fe having an oxidation state of +3
- = to overall charge e.g. sum of oxidation states in SO4^2- is -2
- -1
- +1
- -1
- -2 (-1 if in peroxides such as H2O2
What are redox reactions
Chemical reactions where the oxidation state of one more more species changes
Oxidation and reduction are determined by constructing balanced equations and completing complete ionic equations
Zn(s) +2HCl(aq) –> ZnCl2 (aq) + H2
Zn(s) + 2H+(aq) + 2Cl-(aq) –> Zn2+(aq) + 2Cl^-1(aq) + H2
Zn is oxidised (0–> +2), H in HCl is reduced (+1–>0)
Half equations for oxidation and reduction
Oxidation: Zn(s)–>Zn^2+ (aq) + 2e-
Reduction: Cu^2+ +2e- –>Cu(s)
Define reductant/reducing agent vs oxidant/oxidising agent:
Reductant/reducing: reactant that undergoes oxidation, reduces another reactant
Oxidant/oxidising: reactant that undergoes reduction, oxidises another reactant
For standard potential, what does the voltage mean
If the potential is positive, reduction half-equation is spontaneous and produces electrical energy
Ag+ + e- –>Ag
Produces 0.8V
If potential is negative, reduction half-equation is non-spontaneous and requires electrical energy
K+ + e- –>K
Requires 2.94V
How to find standard potential for oxidation reactions
When read to right to left, each reaction is an oxidation half-equation
Standard potential for each oxidation reaction is the negative (opposite sign)
Ag–>Ag+ + e- –>
Requires 0.8V
K–>K+ + e-
Produces 2.94 V
Relationship between reactivity and standard reduction table
More reactive a metal, more easier it is oxidised
Less reactive a metal, more easier it is reduced
Relationship between activity series and table of standard reduction
Metals which are more active (based on activity series) also tend to be oxidised easier (i.e their metal ions are more difficult to reduce, and appear higher upon the table of standard reduction potentials
Where does oxidation and reduction occur in galvanic cells?
In electrodes in half cells
Anode: electrode in oxidation half cell
Cathode: electrode in the reduction half cell
What are the electrolytes in half cells
electrolytes are aqueous so that ions can be conducted therefore electricity can be conducted.
Anolyte: electrolyte in the oxidation half cell
Catholyte: electrolyte in reduction half cell
Why must electrical leads be used to transfer electricity
Spontaneous redox reactions involve the transfer of electrons from anode (site of oxidation) to cathode (site of reduction).
Role of salt bridge
Close the electrical circuit to allow electricity flow
Maintain electrical neutrality of each half-cell
Note: salt bridge conducts ions not electrons
Absence of salt bridge would cause what
Net loss of electrons at the anode half cell and net gain at the cathode
Anode becomes more positively charged and cathode more negatively charged
Over time, cell will cease operability due to electrons being repelled against their travel direction.
Describe galvanic cell notation
anode|anolyte||catholyte|cathode
Zn(s)|Zn2+(aq)||Cu2+(aq)|Cu(s)
Zn(s): anode
Zn2+/Zn(NO3)2: anolyte
Cu2+(aq)/Cu(NO3)2 (aq): catholyte
Cu(s): cathode
Two lines indicate salt bridge
Types of galvanic cells
Two reacting electrodes (both electrodes partake in the redox reaction)
Non-reacting electrode (at least electrode doesn’t partake in redox reaction)
For these half cells, use Pt or C (graphite) instead. Also applies for gaseous redox reaction
Gaseous redox reaction (at least one electrode has a gaseous reagent)
How to calculate Ecell
Determine which species will undergo oxidation and reduction,
Determine standard potential for reduction and oxidation reactions
Find total standard potential by adding reduction and oxidation potentials
Note: for a galvanic cell to function, redox reaction must be spontaneous meaning Ecell>0V
Collision theory assumptions
Molecules are spherical in shape
Molecules travel through space in linear fashion
Collisions only occur between two molecules
Collisions are only successful or unsuccessful
Conditions successful collision must satisfy
Molecules must collide with sufficient kinetic energy i.e energy greater than the activation energy
Molecules must collide at the correct orientation
Rate of reaction in equation form
How to increase rate of reaction
Rate of reaction=(freq of collisions per unit volume per unit time) x (success rate of collisions)
Increase freq of collisions per unit volume per unit time
Increase success rate of collisions
State metal reactivity series in descending order
please - potassium(k)
send - sodium(Na)
cats - calcium(Ca)
monkeys - magnesium(Mg)
and - Aluminum(Al)
zebras - zinc(Zn)
in - iron(Fe)
lovely - lead(Pb)
happy - hydrogen
cages - copper(Cu)
made of - mercury(Hg)
silver - silver(Ag)
gold - gold(Au)
In a maxwell-boltzmann distribution graph, what does the area under the graph represent
The total number of particles present, which is a constant for any sample of matter
Define activation energy
Activation energy link with rate of reaction
Minimum energy that molecule must possess in order for it to undergo a successful collision. Expressed in Joules
The rate of reaction increases when more molecules possess kinetic energy exceeding the activation energy
What factors influence the rate of reaction
Catalysts: If a catalyst is introduced, the activation energy decreases which increases the success rate of collisions. By reducing the Ea, the proportion of molecules with E≥Ea increases so the rate of reaction increases
Surface area: If surface area increases, this causes the collisional cross-section area to increase effectively increasing the number of molecules that have the ability to react. Since total frequency of collisions increases, the no of molecules with E≥Ea so rate of reaction increases. However, relative frequency of successful collisions or success rate remains the same.
Concentration: If concentration increases, then more molecules per unit volume will exist, this increases the frequency of collisions which increases the number of molecules with E≥Ea so rate of reaction increases. However, relative frequency of successful collisions, or success rate remains the same.
Temperature: If temperature increases, the total frequency of collisions increase since the molecules have more kinetic energy so they collide more frequently. However, increasing temperature also increases the success rate of collisions unlike SA and concentration. The proportion of molecules with E≥Ea increases since the Maxwell-Boltzmann distribution graph has shifted to the right.
How to increase surface area
Effect on Maxwell-Boltzmann distribution graph
Cut up and crush the solid reagent into smaller pieces
Melt or boil the reagent to convert into a liquid or gas since gases have the highest SA followed by liquids then small solid particles (powder)
This increases the height of the Maxwell-Boltzmann distribution
Effect of concentration increase on Maxwell-Boltzmann distribution
Increases height
Remember only, aqueous and gaseous species concentration can be increased
Effect of temperature increase on Maxwell-Boltzmann distribution
Shifts the peak right since average KE of molecules has increased. Total area under cure remains constant (no of particles haven’t changed). Height of graph must be reduced to abide this. Shifts left if temperature decreases
X and Y axis for Maxwell-Boltzmann distribution graphs and energy profile diagrams
Maxwell-Boltzmann distribution graphs
Y: no of particles
X: KE (J)
energy profile diagrams
Y: Energy
X: progress of reaction
Difference in exothermic and endothermic energy profile diagrams
Endothermic: energy of the products>energy of the reactants since heat has been absorbed from the surroundings
Exothermic: energy of the products<energy of the reactants since heat has been released to the surroundings
How to find w/v percentage and v/v
To get w/v percentage, multiply molarity by molar mass of the substance and divide by 10. To get v/v percentage, multiply molarity by molar mass of the substance and divide by 10 times the mass density of the solution.
How to convert concentration to ppm
If you take molarity (with units mol/L) and multiply it by the molar mass (with units g/mol), you get g/L. Just multiply g/L by 1000 to convert g to mg, and you have ppm (in mg/L of water).
