OCR Chemistry B: Making Useful Chemicals
1. Industrial Chemistry Principles
1.1 Rates of Reaction in Industrial Processes
Rate equations and orders of reaction
Zero order: rate = k
First order: rate = k[A]
Second order: rate = k[A][B] or rate = k[A]²
Rate-determining step: The slowest step in a multi-step reaction mechanism
Activation energy (Ea): Energy barrier that must be overcome for a reaction to occur
Arrhenius equation: k = Ae^(-Ea/RT)
k = rate constant
A = pre-exponential factor
Ea = activation energy
R = gas constant (8.31 J K⁻¹ mol⁻¹)
T = temperature in Kelvin
1.2 Industrial Catalysts
Heterogeneous catalysts: Different phase from reactants (typically solid)
Provide a surface for adsorption
Lower activation energy by providing alternative reaction pathway
Examples: Iron in Haber process, Nickel in hydrogenation, Vanadium(V) oxide in Contact process
Homogeneous catalysts: Same phase as reactants
Examples: Acids in esterification, Enzymes in biological systems
Catalyst properties:
Specificity
Activity
Selectivity
Resistance to poisoning
1.3 Equilibrium in Industrial Processes
Le Chatelier's Principle: System in equilibrium responds to minimize effects of changes
Factors affecting position of equilibrium:
Temperature
Pressure
Concentration
Catalysts (affect rate but not position of equilibrium)
Equilibrium constant expressions:
K<sub>c</sub> = [products]/[reactants] (concentration)
K<sub>p</sub> = (partial pressures of products)/(partial pressures of reactants)
2. Green Chemistry and Sustainability
2.1 Principles of Green Chemistry
Atom economy: (Mr of desired product ÷ Mr of all reactants) × 100%
E-factor: Mass of waste ÷ Mass of product
Waste reduction strategies:
Use of catalysts
Alternative solvents (water, supercritical CO₂)
Renewable feedstocks
Energy efficiency
Batch vs. continuous processes:
Batch: Reactants added, products removed after reaction
Continuous: Reactants continuously added, products continuously removed
2.2 Sustainable Industrial Chemistry
Life cycle assessment (LCA): Cradle-to-grave analysis
Renewable resources:
Biomass
Plant oils
Carbohydrates
Recycling and waste management
Carbon footprint reduction strategies
3. Haber Process for Ammonia Production
3.1 Process Details
Reaction: N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
Conditions:
Temperature: 400-450°C (compromise temperature)
Pressure: 200-300 atmospheres
Catalyst: Iron with promoters (K₂O, Al₂O₃)
Equilibrium considerations:
Exothermic reaction (forward reaction releases heat)
Decrease in number of gas molecules (3:1 ratio)
Low temperature favors yield but slows rate
High pressure favors yield (expensive)
3.2 Ammonia Uses and Environmental Impact
Uses:
Fertilizers (80% of ammonia production)
Production of nitric acid
Explosives
Cleaning products
Environmental considerations:
Energy intensity of production
Nitrogen pollution from fertilizer runoff
Eutrophication
4. Contact Process for Sulfuric Acid Production
4.1 Process Details
Three main stages:
Burning sulfur: S(s) + O₂(g) → SO₂(g)
Catalytic oxidation: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g)
Absorption: SO₃(g) + H₂SO₄(l) → H₂S₂O₇(l), then H₂S₂O₇(l) + H₂O(l) → 2H₂SO₄(l)
Conditions for SO₂ oxidation:
Temperature: 450°C
Catalyst: Vanadium(V) oxide
Pressure: Slightly elevated (1-2 atm)
Equilibrium considerations:
Exothermic reaction
Decrease in number of gas molecules
Low temperature favors yield but slows rate
4.2 Sulfuric Acid Uses and Properties
Uses:
Fertilizer production
Metal processing
Oil refining
Chemical synthesis
Properties:
Strong diprotic acid
Dehydrating agent
Oxidizing agent
Viscous liquid
5. Organic Industrial Chemistry
5.1 Cracking
Thermal cracking:
High temperature (800°C)
Moderate pressure
No catalyst
Produces alkenes and smaller alkanes
Catalytic cracking:
Lower temperature (450°C)
Zeolite catalysts
More branched products
Higher octane products
Steam cracking:
Very high temperature (850°C)
Dilution with steam
Produces ethene for polymerization
5.2 Reforming and Isomerization
Catalytic reforming:
Converts alkanes to aromatic compounds
Platinum/rhenium catalysts
Increases octane rating
Isomerization:
Converts straight-chain alkanes to branched isomers
Aluminum chloride or zeolite catalysts
Improves fuel properties
5.3 Polymers and Plastics Production
Addition polymerization:
Ethene → polyethene
Propene → polypropene
Styrene → polystyrene
Condensation polymerization:
Polyesters: Diacid + diol
Polyamides (nylons): Diacid + diamine
Polymer properties related to structure:
Chain length
Branching
Cross-linking
Crystallinity
6. Laboratory Synthesis Techniques
6.1 Organic Synthesis Pathways
Common functional group interconversions:
Alcohol → aldehyde → carboxylic acid
Alkene → alcohol → halogenoalkane
Nitrile → carboxylic acid
Reaction types:
Addition
Substitution
Elimination
Oxidation
Reduction
6.2 Purification Techniques
Recrystallization:
Solvent selection
Hot filtration
Cooling crystallization
Vacuum filtration
Distillation:
Simple distillation
Fractional distillation
Vacuum distillation
Extraction:
Solvent selection
Separating funnel technique
Back extraction
6.3 Analytical Techniques
Thin Layer Chromatography (TLC):
Retention factor (Rf) calculation
Mobile and stationary phases
Visualization methods
Melting point determination:
Pure compounds vs. mixtures
Depression by impurities
Spectroscopic analysis:
IR spectroscopy for functional group identification
NMR spectroscopy for structural determination
Mass spectrometry for molecular weight and fragmentation pattern
7.1 Calculation Questions
Always include units
Show all working clearly
Round to appropriate significant figures
Common calculations:
Percentage yield
Atom economy
Equilibrium constants
Rate equations
7.2 Extended Response Questions
Structure answers with clear paragraphs
Use chemical terminology accurately
Link theory to practical applications
Balance explanations of scientific principles with industrial context
7.3 Data Analysis Questions
Identify trends in data
Calculate values from graphs and tables
Relate data to chemical principles
Evaluate reliability and validity of data
7. Practice Questions
Calculate the atom economy for the production of ethanol from ethene: C₂H₄ + H₂O → C₂H₅OH
Explain why the Haber process operates at 450°C despite the reaction being exothermic.
Compare and contrast heterogeneous and homogeneous catalysis, giving an industrial example of each.
Describe how the principles of green chemistry can be applied to make the production of sulfuric acid more sustainable.
Explain the importance of the rate-determining step in industrial processes and how catalysts affect it.
Describe and explain the effect of temperature and pressure on the equilibrium yield in the Contact process.
Calculate the percentage yield of a reaction that produces 45g of product when the theoretical yield is 60g.
Discuss the environmental implications of using the Haber process for ammonia production.
Explain how fractional distillation separates crude oil into useful fractions and why this is an important industrial process.
Compare batch and continuous processes in chemical manufacturing, discussing the advantages and disadvantages of each.
8. Key Definitions and Terms
Catalyst: Substance that increases reaction rate without being consumed
Yield: Amount of product obtained from a reaction
Atom economy: Measure of efficiency in terms of atoms used
Equilibrium: State where forward and reverse reaction rates are equal
Activation energy: Minimum energy required for a reaction to occur
Fractional distillation: Separation technique based on boiling point differences
Cracking: Breaking large hydrocarbons into smaller, more useful molecules
Green chemistry: Design of chemical products and processes that reduce or eliminate hazardous substances
Sustainability: Meeting present needs without compromising future generations
Life cycle assessment: Evaluation of environmental impacts of a product throughout its life
9. Common Exam Misconceptions
Catalysts do not change the position of equilibrium, only the rate at which it is reached
Higher temperature does not always mean higher yield (depends on reaction thermodynamics)
Percentage yield and atom economy measure different aspects of reaction efficiency
Industrial conditions are often compromises between rate, yield, and economic factors
Sustainability involves more than just environmental considerations