Chemistry Unit 3 Flashcards
State how industrial processes are designed
Industrial processes are designed to maximise profit and minimise the impact on the environment.
Factors influencing industrial process design
Availability, sustainability and cost of feedstock
Opportunities for recycling
Energy requirements
Marketability of by-products
Product yield
State what environmental factors are taken into consideration when designing industrial processes
Minimising waste
Avoiding the use or production of toxic substances
Designing products which will be biodegradable if appropriate
Balance an equation
When balancing an equation there must be the equal numbers of every atom on each side of the equation.
Balance an equation stages
- Write down how many of each atom there is on either side of the equation
- Balance each atom in turn
Calculate the mass of any substance using n=m/GFM step 1
Write down the formula (always check the data booklet) and what you know from the question.
Calculate the mass of any substance using n=m/GFM step 2
Substitute in values.
Calculate the mass of any substance using n=m/GFM step 3
Calculate or check units.
Calculate the number of moles, volume or concentration step 1
Write down the formula and the values given in the question.
n = c × V
Calculate the number of moles, volume or concentration step 2
Substitute in the values.
Calculate mass, concentration, volume or number of moles from a balanced equation step 1
Write down what you know from the question
Calculate mass, concentration, volume or number of moles from a balanced equation step 2
Using the formulas from the data booklet calculate the number of moles
Calculate mass, concentration, volume or number of moles from a balanced equation step 3
Use the mole ratio to determine the n of the desired substance.
Calculate mass, concentration, volume or number of moles from a balanced equation step 4
Substitute the values into the formula to calculate the unknown value.
State the formula for calculating the molar volume
molar volume = volume/no of moles
what is the molar volume
Molar volume is the volume occupied by one mole of any gas. This means that under the same temperature and pressure, one mole of any gas will occupy the same volume.
how to calculate a ratio
Using this theory and a balanced equation, if you have the volume of one gas, you can calculate (using ratios) the volume of the other gases
what is the %yield
The % yield is used to compare the yield of a product actually obtained with what could have been obtained in theory (if all of the reactants were converted with no waste).
how to calculate the %yield
%yield= actual yield/theoretical yield x 100
what is %atom economy
The % atom economy is a measure of the % of reactant that become useful products. Atom economy tends to be used more in industry as it tells chemists how efficient a process actually is.
how to find the %atom economy
%atom economy = mass of desired product from equation/total mass of products from equation x 100
what is a limiting reactant
the reactant in a chemical reaction which is used up when the reaction stops.
what is an excess reactant
the reactants which are ‘left over’ at the end of a reaction.
step 1 of the percentage yield
Find the actual yield (always given in the question).
step 2 of the percentage yield
Write the mole ratio below them.
step 3 of the percentage yield
Work out the theoretical yield from the equation. (the gfm) then divide them by eachother to find 1 gram and times by the amount of grams used now put into the equation
stages of atom economy
- Underline your desired product
- Write the masses of all chemicals below
- Work out atom economy using the equation
Explain why reaction rates must be controlled in industrial processes
If reaction rates are too low, the process will be not economical.
If reaction rates are too high, there will be a risk of explosion.
how does concentration effect reaction rates
there are more particles in the reaction leading to more chance of collisions.
Calculate the relative rate of a reaction
relative rate = 1/t
how does particle size effect reaction rates
decreasing the particle size allows more ‘space’ for collisions (due to increase in surface area).
how does temperature effect reaction rates
increasing the temperature, the particles have more energy so move faster (collisions more likely).
how does pressure effect reaction rates
if pressure is increased (for gaseous reactants) there are more reactant particles for a given volume so there will be more collisions.
how does collision geometry reaction rates
particles must collide with the correct geometry for the reaction to be successful
exothermic graph
Energy of the product is less than the energy of reactants (energy given out to surroundings) giving a -ve enthalpy.
endothermic graph
Energy of products is more than the energy of reactants, giving a +ve enthalpy.
Enthalpy change definition
Enthalpy change is the difference in energy between the products and reactants.
Exothermic reactions = negative enthalpy
Endothermic reactions = positive enthalpy
activation energy
Activation energy (Ea) is the minimum energy required by the particles to form an activated complex. If colliding particles don’t have the activation energy, the collision will not take place.
what is the activated complex
Activated complex is the unstable arrangement of atoms formed at the top of the potential energy barrier (at top of the graph).
how does a catalyst effect activation energy
Catalysts provide an alternative pathway for reactants. The alternative pathway will have a lower activation energy. This means that more particles will have sufficient energy to collide
what do energy distribution diagrams show
Energy distribution diagrams show the number of molecules and the energy they have.
how is the activation energy shown on a graph
The activation energy is often shown as a dotted line on the diagrams. Only the particles with energy above the Ea will take part in the reactions.
what does increasing temperature do to particles
Increasing the temperature means that the particles will have more energy, so therefore more of them will reach the activation energy.
what does adding a catalyst do to activation energy
Adding a catalyst will lower the activation energy - therefore more particles will reach it.
what is enthalpy
Enthalpy is a measure of the chemical energy in a substance (measured in kJ).
how does exothermic effect industry
releases heat energy to the surroundings. In industry it may require excess heat to be removed to prevent extreme temperature rises or dangerous conditions.
how does endothermic effect industry
takes in heat energy from the surroundings. In industry there may be costs involved in supplying heat at the start of the reaction and also in maintaining the reaction rate.
what is the enthaply formula
Eh = cm∆T
what is enthalpy of combustion
Enthalpy of combustion is the energy change when one mole of the substance burns completely in oxygen.
what does hesses law state
Hess’s Law states that the enthalpy change for a reaction depends on the initial and final states of the reaction and is independent of the route the reaction occurs.
what does hess law mean
This means that no matter the route taken, the enthalpy change will always be the same for a reaction. Knowing this we can calculate enthalpy.
step 1 of hess law
Write down the equation for which you want to find the enthalpy
step 2 of hess law
Write out the equations and values of the enthalpies of combustion of the other reactants
step 3 of hess law
Compare with the desired equation and rearrange where necessary
step 4 of hess law
Cancel out and calculate the enthalpy
what is molar bond enthalpy
Molar bond enthalpy is the energy required to break one mole of bonds in a diatomic molecule.
what is mean molar bond enthalpy
Mean molar bond enthalpy is the energy required to break one mole of bonds that occur in compounds (not diatomic).
The mean is used for certain bonds as the energy required differs depending on where the bond is found (position in compound, other atoms around it, etc).
what is dynamic equilibrium
Dynamic equilibrium is when the rates of a forward and reverse reaction are equal.
what is closed system in equilibrium
Closed system is when the reaction is carried out in a sealed container, so no reactants or products are lost.
Concentrations of reactants and products at equilibrium
At equilibrium the concentrations of reactants and products are constant but not necessarily (in fact rarely) equal.
Describe why chemists move the position of equilibrium
Chemists in industry often move the position of equilibrium to favour the products and to maximise their profits.
what is the haber process
uses high pressure to favour the products (less gaseous molecules) and a medium temperature (forward reaction is exothermic so favours low temperatures, however too low would cause the rate to be slower, and therefore not as profitable).
how does tempreture effect equilibrium
Increasing the temperature favours the endothermic reaction - shift in the endothermic direction.
Decreasing the temperature favours exothermic reaction - shift in the direction of the exothermic reaction.
how does pressure effect equilibrium
Changing pressure ONLY affects substances that are in a gaseous state.
Increasing the pressure favours the side with LOWER gas volume.
Decreasing the pressure favours the side with HIGHER gas volume.
how does Adding/removing reactants/products effect equilibrium
Adding a reactant (or removing a product) - will shift equilibrium to the right (this is to compensate the gain/loss).
Adding product (or removing a reactant) - shift the equilibrium to the left.
Neutralisation reactants can affect equilibrium if the equation contains hydrogen (H+)ions or hydroxide (OH-) ions.
Effect of catalysts on equilibrium
Catalyst have no effect on equilibrium position. They will allow equilibrium to be reached quicker and at a lower temperature.
how does chromatography work
Chromatography is used to separate substances in complex mixtures. It works as substances travel at different speed (due to size, polarity etc).
Describe how components can be identified using chromatography
Components can be identified by the distance they have travelled or by the time it has taken to travel through the apparatus (retention time).
Understand the graphical results of a chromatography experiment
On a graph, the quantity of a substance is shown on y-axis, and the retention time on the x-axis.
Describe the term volumetric analysis
Volumetric analysis uses a solution of accurately known concentration in a reaction to determine the concentration of another.
State the use of titration experiments
Titrations are used to accurately determine the volumes of solution required to reach the end point of a chemical reaction. Knowing this volume can then lead to calculating concentrations.
Describe the term standard solution
Standard solution is a solution of accurately known concentration.
State the use of redox titrations
Redox titrations are titrations based on redox reactions and used to determine the unknown concentration of a solution.
Explain why indicators are not always needed to determine end-points of reactions
In some titrations an indicator is not required as the solution may self-indicate (change colour itself). For example, acidified permanganate is purple but turns colourless when reduced.
What is the collision theory?
For a chemical reaction to occur, the reactant molecules must collide with enough energy
