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What is rate of reaction?
How fast a reaction is occuring
How can rate of reaction be calculated?
Measuring the formation of products over time or how quickly reactants are used up
What are the 2 equations for rate of reaction?
Quantity of reactant used ÷ time taken = mean rate of reaction
Quantity of products formed ÷ time taken = mean rate of reaction
What are the following factors that affect rate of reaction?
Temperature
Concentration (for solutions)
Pressure (for gases)
Surface area
Catalyst
What is the collision theory?
In order for a reaction to occur, particles must collide with enough energy called activation energy
What is activation energy?
Minimum energy needed for a reaction to occur
How does increasing temperature increase the rate of reaction?
Increases the kinetic energy of the particles, making them move faster. This increases the frequency of collisions which increases the rate of reaction. The same amount of products are made, just faster
Also gives more activation energy, so more collisions are successful
How does increasing concentration/pressure increase the rate of reaction?
Increases the number of particles in a given volume
This increases the frequency of collisions which increases the rate of reaction
Changing the concentration affects the amount of products formed
How does increasing surface area increase the rate of reaction?
More particles are exposed
This increases the frequency of collision which increases the rate of reaction
The same amount of products are made, just faster
How does catalysts increase the rate of reaction?
Provides an alternative route with a lower activation energy
This increases the rate of reaction
The same amount of products are made, just faster
Using the rate of reaction graph, describe what is happening at the point where the arrow is point at
There is a fast rate of reaction here as there is lots of reactant particles available, so higher concentration of reactant particles, so more frequent collisions
Using the rate of reaction graph, describe what is happening at the point where the arrow is point at
There is a slow rate of reaction here due to reactants being used up, so lower concentration of reactant particles, so less frequent collisions
Using the rate of reaction graph, describe what is happening at the point where the arrow is point at
The reaction is over as one or both reactants are used up
How would you calculate rate of reaction at 20s using a graph?
Draw a tangent to the curve at 20s
Then, calculate the gradient of the tangent
Mg(s) + HCl(aq) → MgCl2(aq) + H2(g)
How to measure the rate of reaction when the gas is a product?
Measure 25cm³ of hydrochloric acid using a measuring cylinder and then put it into a conical flask
Measure 3cm length piece of magnesium ribbon
Place the magnesium ribbon into the flask and immediately place the bung on top
Start the timer and take readings of the volume of gas at regular intervals (every 10 sec up to 100 sec)
Repeat the experiment but you change the independent variable (concentration of hydrochloric acid)
Plot onto a graph (a and b are 2 variations of the experiment, different concerntrations)
What are the control variables in measuring the rate of a reaction when a gas is a product?
Volume of the solutions
Concentration of the solutions
Mass of solid
Temperature
Na2S2O3(aq) + HCl(aq) → NaCl(aq) + S(s) + SO2(g) + H2O(l)
How to measure the rate of reaction when the solid is a product?
Measure 50cm³ of sodium thiosulphate using a measuring cylinder and put it into a conical flask placed on a black cross
Measure 10cm³ of hydrochloric acid using a different measuring cylinder and pour it into the conical flask and start the timer
Stop the timer when the cross is no longer visible, and then plot the results
Repeat the experiment but you change the independent variable (Concentration of hydrochloric acid by 0.5)
NO GRAPHS ARE IN THIS!!!!
What are the control variables in
measuring the rate of a reaction when a solid is a product?
Volumes of the solutions
Concentration of the solutions
Temperature
What is a dynamic equilibrium?
Where the forward and backward reaction occur at the same rate, causing no change in concentration of reactants and products
What kind of system does dynamic equilibrium only occur in?
A closed system ( no reactants and products can escape)
Explain how a dynamic equilibrium occurs?
Initially, forward reaction faster than backward reaction due to higher conc. of reactants
Over time, conc. of reactants decrease and conc. of products increase
This means rate of forward reaction decreases, rate of forward reaction increases, until both are same
What does Le Chatelier’s principle state? and give an example
When an equilibrium will shift to oppose any change placed on the system e.g. if temperature has been increased, equilibrium will shift to decrease temperature
Looking at the equation, what would happen if the concentration of hydrogen was increased?
N2(g) + 3H2(g) ⇌ 2NH3(g)
Equilibrium will shift to the right to decrease conc. of hydrogen, meaning there would be a greater yield of NH3
Looking at the equation, what would happen if the concentration of NO2 was decreased?
N2O4(g) ⇌ 2NO2(g)
Equilibrium will shift to the right to make more NO2 , so yield of NO2 would increase
Looking at the letter equation, what would happen if the concentration of C was increased?
A(aq) + B(aq) ⇌ C(aq) + D(L)
Equilibrium will shift to the left to decrease conc. of C
Looking at the letter equation, what would happen if the concentration of D was decreased?
A(aq) + B(aq) ⇌ C(aq) + D(L)
Equilibrium will shift to the right to increase conc. of D
This equation is a forward reaction that is exothermic, what would happen if the temperature was increased?
N2(g) + 3H2(g) ⇌ 2NH3(g)
Equilibrium will shift in backward direction as it’s endothermic. Yield of NH3 would decrease as a result
This equation is a forward reaction that is endothermic, what would happen if the temperature was increased?
N2O4(g) ⇌ 2NO2(g)
Equilibrium will shift in forward direction as it’s endothermic. Yield of NO2 would increase as a result
This equation is a forward reaction that is endothermic, what would happen if the temperature was decreased?
CaCO3(s) ⇌ CaO(s) + CO2(g)
Equilibrium will shift in backward reaction as it’s exothermic. Yield of CaO would decrease as a result
Looking at the equation below, what would happen if the pressure was increased?
N2(g) + 3H2(g) ⇌ 2NH3(g)
There are 4 molecules on LHS of arrow and 2 molecules on RHS of arrow. If pressure was increased, equilibrium will shift to the right, as right hand side has less molecules. This increases yield of NH3
Looking at the equation below, what would happen if the pressure was decreased?
N2O4(g) ⇌ 2NO2(g)
There is 1 molecule on LHS of arrow and 2 molecules on RHS of arrow. If pressure was decreased, equilibrium will shift to the right, as right hand side has more molecules. This increases yield of NO2
Looking at the equation below, what would happen if the pressure was changed?
H2(g) + I2(g) ⇌ 2HI
There are same number of molecules on both sides, no effect on the position of the equilibrium and yield of HI
What is crude oil and how is it formed?
Finite resource (will run out) formed from the remains of dead plankton compressed under mud over millions of years
How is coal formed?
Formed from the remains of trees compressed under mud over millions of years
What is limestone and how is it formed?
Sedimentary rock made of sand, silt and marine organisms compressed over the millions of years
What is crude oil a mixture of?
Different chains of hydrocarbons (compound of carbon and hydrogen atoms)
Most of the hydrocarbons in crude oil are chemicals called…
Alkanes
What are alkanes? (NOT THE SAME AS ALKENES!)
A homologous series (family of compounds with similar properties and same general formula) of saturated hydrocarbons
What happens if a hydrocarbon is saturated (alkane)?
It will only contain C-C bond
What is the general formula for alkanes?
CnH2n+2
What are the alkanes that you will need to know for your GCSE exams?
What is combustion?
The burning of fuel in the presence of oxygen to produce energy
What is complete combustion?
Where the fuel is burnt completely in oxygen to form CO2 and water
e.g. propane + oxygen → carbon dioxide + water
What is incomplete combusion?
Where the fuel is burnt in limited oxygen and can also form carbon particulates, carbon monoxide and water
e.g. propane + oxygen → carbon dioxide + carbon + carbon monoxide + water
What is the method used to seperate different fractions of crude oil?
Fractional distillation
How to do fractional distillation?
Crude oil is heated and turned into a vapour
Vapours enter fractionating column where it is hotter at top and cooler at bottom
Different fractions cool and condense at different points based on boiling points
What does a fractionating column look like?
What happens if carbon chains get longer?
Boiling point increases as they have stronger intermolecular forces
Becomes less flammable (harder to ignite)
Become more viscous (more thick and less runny)
What are alkenes? (NOT THE SAME AS ALKANES!)
A homologous series (family of compounds with similar properties and same general formula) of saturated hydrocarbons
What happens if a hydrocarbon is unsaturated (alkene)?
It will contain at least one C=C double bond
Alkenes have double bonds, what happens to them? And how do you test for alkenes?
It becomes more reactive and will react with bromine water, turning it from orange to colourless. This is the test for alkenes
What are alkenes used to make?
Polymers
What is cracking?
Breaking a longer chain hydrocarbon into a smaller chain hydrocarbon and alkenes
What are the 2 types of cracking?
Steam cracking
Catalytic cracking
What is steam cracking?
Cracking carried out under high temperatures and high pressure
What is catalytic cracking?
Cracking carried out at low temperatures and a catalyst (zeolite) is used to speed up the rate of reaction
Why is catalytic cracking preferred over steam cracking?
Low costs
Low energy consumption
Makes more shorter chain alkanes
Why is cracking important after fractional distillation?
After fractional distillation, there is not enough shorter chain hydrocarbons needed for fuels
To meet demand, the excess longer chain hydrocarbons are cracked
The shorter chain hydrocarbon is used as fuel, and the alkenes are used to make polymers
What is a compound?
2 or more different atoms chemically joined together
What is a mixture?
2 or more different substances mixed but not joined together
What is a formulation?
Mixtures designed as a useful product e.g. medicines and paints
How does filtration separate mixtures?
The insoluble solid is too big to go through holes on filter paper, causing the separation of the insoluble solid from the solvent
How does evaporation separate mixtures?
The solvent has a lower boiling point so it turns into a gas, causing the separation of the soluble solid from the solvent
How does distillation separate mixtures?
The liquid with the lower boiling point evaporates and condenses first, causing the separation of 2 different liquids
How does chromotography separate mixtures?
The different dyes have different solubilities so they move different distances up the paper, causing the separation of multiple soluble solids (colours) from a solvent
What do pure substances only contain?
One type of substance, it is made up of only one type of element or compound
What changes happen to substances when they become impure?
Boiling point increases
Melting point decreases
Range of boiling points between different substances
How to do the test for hydrogen?
Place a burning splint at the opening of a test tube, if hydrogen gas is present, it will burn rapidly with a squeaky pop sound
How to do the test for oxygen?
Place a glowing splint inside a test tube, the splint will relight in the presence of oxygen
How to do the test for carbon dioxide?
When carbon dioxide is shaken with limewater, the limewater turns cloudy
How to do the test for chlorine?
If chlorine is present within the litmus paper, the litmus paper should become bleached and turn white
How to do the chromotography required practical?
Draw a pencil line, using a ruler, 2cm from the bottom of the chromatography paper. Line in pencil as this does not run up the paper
Add the soluble solids (ink) on the line
Place the chromatography paper in the beaker with the pencil line above the water level. Otherwise, the ink will dissolve into the water
Allow the water to move up the paper and carry soluble solids with it
Allow the paper to dry and then calculate Rf values using the equation below
Distance travelled by substance ÷ distance travelled by solvent = Rf
What is the equation for Rf ?
Distance travelled by substance ÷ distance travelled by solvent = Rf
By looking at the chromatogram, can you explain what happened with the black ink?
The chromatogram shows that the black ink is a mixture as there are multiple dots (4) in the same column
The black ink contains blue ink, green ink, and yellow ink as they have dots in the same horizontal row
It also contains an unknown ink
By looking at the chromatogram, why does the yellow ink move further up the paper?
The yellow ink moves further up the paper because it is more attracted to the mobile phase (water) and less attracted to the stationary phase (paper). This means it is more soluble and therefore carried further up the paper
By looking at the chromatogram, can you give the Rf value for the green ink?
8/10 = 0.8
During chromotography, what do you do if the dot doesn’t move up the paper?
Use a different solvent as the dot is insoluble in the solvent
What are the gases in the atmosphere and give the percentages?
Nitrogen 78%
Oxygen 21%
Argon 0.9%
Carbon dioxide 0.04%
All other gases 0.06%
What was the early earth’s atmosphere made up of? And what caused this?
Predominantly carbon dioxide and water vapour
Little bits of methane, nitrogen and ammonia
Caused by intense volcanic activity
How did the early earth’s atmosphere change to today’s atmosphere?
Volcanoes became inactive, causing a decrease in temperature
this causes water vapour to cool and condense to form oceans and seas
Carbon dioxide levels decreased as it dissolved in oceans and got locked up in sedimentary rocks
Plants and algae evolved to photosynthesis, decreasing carbon dioxide levels further and increasing levels of oxygen in the air
Nitrogen levels increase as ammonia becomes oxidised and turns into nitrogen.
What are the 3 main greenhouse gases?
Carbon dioxide
Methane
Water vapour
Is the greenhouse effect essential?
Yes as the greenhouse effect makes sure the earth doesn’t become too cold. Due to rising levels of carbon dioxide and methane, we now have the enhanced greenhouse effect
Explain how the greenhouse effect works
The earth absorbs short-wavelength infrared radiation from the Sun, warming up the surface
Earth emits infrared radiation of different longer wavelengths
These are absorbed by the greenhouse gases, preventing them from escaping into space
This increases average global temperatures.
Why has carbon dioxide levels increased?
Combustion of fossil fuels
Decomposition of increased waste
Deforestation
Why has methane levels increased?
Rice and cattle farming
Decomposition of increased waste
What happens if the sea levels rise due to the melting ice caps?
This causes flooding, destruction of habitats and possible extinction
Extreme weather patterns leading to flooding and droughts
Food and water shortages
Increase in diseases like malaria
Change in species behaviour, such as bird migration patterns
What is carbon footprint?
Total carbon emissions during the life cycle of a product or service
How can carbon footprint be reduced?
Alternative energy resources
Less fossil fuels
Carbon tax/licences
Carbon capture/storage
Why is reducing carbon footprint limited?
Limited by a lack of…
Reliable alternative energy sources
Co-operation from certain countries
Public knowledge and economic considerations
How does the pollutant, carbon dioxide, form and what can it cause?
Formation: complete combustion of carbon-based fuels
Causes: global warming
How does the pollutant, carbon monoxide, form and what can it cause?
Formation: incomplete combustion of carbon-based fuels
Causes: Stops red blood cells from carrying oxygen
How does the pollutant, carbon particulates, form and what can it cause?
Formation: incomplete combustion of carbon based materials
Causes: asthma, global dimming, makes buildings dirty
How does the pollutant, nitrogen oxide, form and what can it cause?
Formation: nitrogen from air reacts with oxygen at high temperatures
Causes: acid rain, asthma/respiratory problems
How does the pollutant, sulfur dioxide, form and what can it cause?
Formation: sulfur from fuel reacts with oxygen at high temperatures
Causes: acid rain which damages limestone buildings and kills aquatic life
What are finite resources?
Ones that are not replenished at the same rate as they are being used e.g. crude oil, metals
What are renewable resources?
Ones that are replenished at the same rate as they are being used e.g. crops
What do humans use earth’s resources for?
Warmth
Shelter
Transport
Food
How do humans supplement natural resources?
By agriculture, in order to provide food, timber, clothing and fuels
What is sustainability?
Meeting the needs of the people today whilst also thinking about the needs of the future generations
What are the three R’s and what do they teach?
They teach ways of ensuring finite resources last as long as possible
Reducing use
Reuse
Recycling
