OCR Chemistry B: Making Useful Chemicals

Zero order reaction

Rate = k, independent of the concentration of reactants.

First order reaction

Rate = k[A], directly proportional to the concentration of one reactant.

Second order reaction

Rate = k[A][B] or Rate = k[A]², depends on the concentration of one or two reactants.

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) describes the relationship between rate constant and temperature.

Heterogeneous catalysts

Catalysts that are in a different phase than the reactants, usually solid.

Homogeneous catalysts

Catalysts that are in the same phase as the reactants.

Le Chatelier's Principle

A system in equilibrium will adjust to minimize the effects of changes.

Equilibrium constant (Kc)

Kc = [products]/[reactants], measures concentrations at equilibrium.

Atom economy

(Mr of desired product ÷ Mr of all reactants) × 100%, measures efficiency.

E-factor

Mass of waste produced per mass of product, indicates wastefulness.

Batch process

Reactants are added, and products are removed after the reaction is complete.

Continuous process

Reactants are continuously added and products are continuously removed.

Life cycle assessment (LCA)

Cradle-to-grave analysis of environmental impacts of a product.

Ammonia (NH₃) production

Haber process involves N₂(g) + 3H₂(g) ⇌ 2NH₃(g) under specific conditions.

Haber process conditions

Temperature: 400-450°C, Pressure: 200-300 atm, Catalyst: Iron.

Contact process for sulfuric acid

Production process involving three main stages: burning sulfur, oxidation, and absorption.

Thermal cracking

Cracking at high temperatures (800°C) without a catalyst.

Catalytic cracking

Cracking using zeolite catalysts at lower temperatures (450°C) to produce branched products.

Addition polymerization

Process where ethene is converted into polyethene.

Condensation polymerization

Process where diacid and diol react to form polyesters.

Purification: Recrystallization

Technique involving solvent selection, hot filtration, and cooling for purification.

Distillation

Separation technique based on differences in boiling points.

Thin Layer Chromatography (TLC)

Techniques used for analyzing compounds by separating them on a layer.

Spectroscopic analysis

Methods like IR, NMR, and mass spectrometry for identifying chemical structures.

Yield

Amount of product obtained from a reaction.

Cracking

The process of breaking large hydrocarbons into smaller, useful molecules.

Green chemistry

Design of chemical products to reduce or eliminate hazardous substances.

Sustainability

Meeting present needs without compromising future generations.

Fractional distillation

A separation technique based on differences in boiling points.

Common exam misconception: Catalysts

Catalysts increase reaction rate but do not change equilibrium position.

Thermodynamics in equilibrium yield

Higher temperature does not always mean higher yield; it depends on reaction specifics.

Percentage yield vs. atom economy

They measure different aspects of reaction efficiency.

Industrial conditions

Often a compromise between rate, yield, and economic factors.

Environmental considerations

Sustainability involves more than just environmental impacts.