Unit 3 Flashcards
7 factors that influence the design of a chemical process
- Cost of feedstock
- Availability of feedstock
- Sustainability of feedstock
- Product Yield
- Opportunities for recycling
- Energy requirements
- Marketability of by-products
Feedstock
A substance from which other chemicals can be produced
Role of nitrogen in feedstock
Used to produce ammonia
Importance of Ethanol
Used to make ester ethyl ethanoate
Information on the cost of feedstock (Cheap)
-Nitrogen is obtained from air, salts are obtained from sea water which is cheap and plentiful
Information of the availability of feedstock
Metal ores have to be mined and transported a long way, adding cost and environmental considerations
Sustainability of feedstock
- How long a feedstock is likely to last
- If it’s a limited supply it can only be produced from one raw material, the cost will be high
Raw Materials
A naturally occurring substance that can be converted into feedstock
Important Raw Materials
Fossil fuels, metal ores, air and water, biomass (Animals and plant material)
High product yield
Allows more profit to be made
Opportunities for recycling
Recycling unreacted reactants saves money and reduced waste
Energy requirements
- The heat produced during exothermic reactions can be used to heat reaction vessels and buildings which save money
- Using a catalyst lowers the temperature and cost of heating
- Endothermic reactions require heating which is costly
Marketability of by-products
- Useful by-products are sold to increase profit
- Toxic by-products can be costly to dispose of safely
Environmental Considerations
Strict codes of conduct must be followed to ensure that chemicals and processes used have minimum impact on the environment
Three main environmental considerations
- Minimising Waste
- Avoiding use of production of toxic substances
- Designing biodegradable products
GFM Triangle of Knowledge
m = n x GFM
Volume Triangle of Knowledge
n = c x v
How to change the volume if given in ml or cm3
Divide by 1000
Triangle of Knowledge for molar volume
v = n x Vmol
Atom Economy
(Mass of Desired Products / Total mass of reactants) x 100
Advantages of a higher AE
Lower the waste, more ‘green’, more efficiently expensive raw materials are used
Percentage Yield
(Actual Yield/Theoretical Yield) x 100
In PY, reasons why it wouldn’t be 100%
- The product may be lost during purification
- The reaction may have side reactions which compete with the desired products
Displacement Reactions
An element higher up the electrochemical series displaces an element lower in the series from a solution of it’s ions
Reducing Agents
- Allows other substances to get reduced
- The reducing agents gets oxidised and donates (lose) electrons
Oxidising Agents
- Allows other substances to get oxidised
- The oxidising agent get reduced and accepts electrons
Rules for writing redox equations
- Identify the two reactants
- Start at the top of list on pg12 of your databook and work down till you come to reactant
- Continue down the list until next reactant
The enthalpy of combustion
The energy released during the complete combustion of 1 mol of a substance
The enthalpy of formation
The change in energy associated with the formation of 1mol of a compound from it’s elements in their standard states
The enthalpy of solution
The energy change associated with dissolving 1mol of the solute in water
Calculating the enthalpy of combustion
- Eh = mc ΔT
2.The number of moles so, n=m/gfm OR n=c x v - ΔH = Eh/n
‘+’if endothermic and ‘-‘ if exothermic
Reasons why values of enthalpy might be different from the databook
- Heat loss to it’s surroundings, a lower value of ΔT
- Incomplete combustion of alcohol
- Loss of alcohol through evaporation
Calculating Hess’s Law (With Cycle)
- Write target equation
- Fit all the information needed for the calculation into a cycle
- Solve the calculation by applying Hess’s Law
Calculating Hess’s Law (With Equations)
- Write out target equation
- Write out the equation for the enthalpy change you are trying to find
- Put a tick by each equation that is going in the right direction and change the sign of the enthalpy change if the equation needs to be reversed to fit the target equation
- Apply Hess’s Law
Hess’s Law
This states that the enthalpy change for a chemical reaction is independent of the route taken
Molar bond enthalpy
The energy needed to break one mole of bonds to form separate atoms in the gaseous state
Going to completion
The reactions only go in the forward direction and keep going until one of the reactions is used up
Reversible Reaction
The products of the reaction can react/ decompose to reform the reactions
Equation for the Haber Process
N2(g) + 3H2(g) ↔ 2NH3(g)
Hydrated Cobalt Chloride
The crystals contain water molecules
Chemical formula for Hydrated Cobalt Chloride
CoCl2.6H20
What happens when hydrated cobalt chloride is heated (Colour Change)
Bright pink to blue
What blue substance is formed when hydrated cobalt chloride is heated
Anhydrous Cobalt Chloride (CoCl2)
Equation for hydrated cobalt chloride and anhydrous cobalt chloride
CoCl2.6H2O(s) ↔ CoCl2(aq) + 6H20(l)
A reversible reaction has reached a state of equilibrium
The rate of the forward and reverse reaction become equal
During equilibrium what happens to the concentration of reactants and products
They remain constant
Are products and reactants equal concentration at equilibrium
No, they’re usually different
Closed system at equilibrium
No reactants or products are added or removed, i.e. if it’s gases then they’re stopped from escaping
The reversible equation of water
H20(l) ↔ H+(aq) + OH-(aq)
Where does the equilibrium lie in the water equation and why?
It lies to the left as there’s a higher concentration of reactants to products
Factors that affect equilibrium
Concentration, Temperature and Pressure
Conclusion for increasing the reactant concentration
By increasing the reactant concentration it shifts the equilibrium to the right as the rate of the forward reaction increases to remove the reactant again
Conclusion for increasing the product concentration
By decreasing the reactant concentration/ increasing the product concentration it shifts the equilibrium to the left as the rate of the reverse reaction increases to produce more reactant
Halide Ions
F-, Cl-, Br-, I-
What happens to the equilibrium in a rise in temperature
A rise in temperature will shift the equilibrium in the direction of the endothermic reaction to remove heat and make the temperature fall again
What happens to the equilibrium when there’s a fall in temperature
A fall in temperature will shift the equilibrium in the direction of the exothermic reaction to produce more heat and make the temperature rise again
What would be the reason(s) for pressure to change the position of the equilibrium
- It involves gases
- There’s different numbers of moles in gaseous reactants(s) and products(s)
Conclusion Marks for concluding pressure changes
Mark 1= State the position of the equilibrium
Mark 2= Discuss whether the rate of the forward reaction or the rate of the reverse reaction has increased
How does a catalyst affect the equilibrium
It doesn’t alter the position of the equilibrium or the value of ΔH but it increases the rate at which the equilibrium is reached.
In Chromatography, why is there differences in polarity and/or size of molecules
They’re exploited to separate the components within a mixture
Retention Time
Depending on the type of chromatography in use, the identity of a component can be indicated either by the distance it’s travelled or by the time it takes to travel through the apparatus
How can chromatography results be represented?
By showing an indication of the quantity of substance present on the y-axis and retention time on the x-axis.
Volumetric Analysis
Using a solution of accurately known concentration in a quantative reaction to determine the concentration of another substance
Standard Solution
A solution of accurately known solution
The end-point
The point at which the reaction is just complete
What does titration determine
The volume of reactant solution required to complete the reaction
Indicator
A substance that changes colour at the end-point
