chemistry specification

4.6 The Rate and Extent of Chemical Change

• Chemical reactions can occur at vastly different rates.

• Reactivity of chemicals significantly affects reaction speed.

• Multiple variables can be manipulated to optimize reaction rates and yields of desired products.

• Energy changes during chemical reactions are crucial for understanding these processes.

• Chemists and engineers in industry optimize these variables to produce sufficient product timely and energy-efficiently.

4.6.1 Rate of Reaction

4.6.1.1 Calculating Rates of Reactions

• Rate of a reaction can be calculated by:

  • Mean Rate of Reaction = Quantity of Reactant Used / Time Taken

  • Mean Rate of Reaction = Quantity of Product Formed / Time Taken

• Reactant/product quantities measured by mass (g) or volume (cm³).

• Rate units may be in g/s or cm³/s; Higher Tier students use moles (mol/s).

• Skills to develop:

  • Calculate mean rates from provided data.

  • Draw and interpret graphs of reactant/product quantity against time.

  • Draw tangents to graph curves and calculate slopes for reaction rates.

4.6.1.2 Factors Affecting Reaction Rates

• Factors impacting reaction rates include:

  • Concentration of reactants

  • Pressure of gases

  • Surface area of solids

  • Temperature

  • Presence of catalysts

• Importance of practical investigations (e.g., changing concentration and measuring gas volume or color change).

4.6.1.3 Collision Theory and Activation Energy

• Collision Theory: Reactions occur when particles collide with sufficient energy.

• Activation Energy: Minimum energy required for a reaction.

• Increasing concentration, pressure, and surface area raises collision frequency and reaction rates.

• Rising temperature increases collision frequency and energy of collisions.

4.6.1.4 Catalysts

• Catalysts enhance reaction rates without being consumed.

• Different reactions necessitate different catalysts (e.g., enzymes in biology).

• Catalysts provide alternative pathways with lower activation energy.

• Students should identify catalysts based on their effects on reactions.

4.6.2 Reversible Reactions and Dynamic Equilibrium

4.6.2.1 Reversible Reactions

• Certain chemical reactions enable products to reform into original reactants (A + B ⇌ C + D).

• Reaction conditions modify the direction of these reactions.

4.6.2.2 Energy Changes in Reversible Reactions

• Exothermic reactions release energy in one direction; endothermic reactions absorb energy in the reverse.

4.6.2.3 Equilibrium

• Equilibrium arises when forward and reverse reactions occur at equal rates in a closed system.

4.6.2.4 Effects of Changing Conditions on Equilibrium

• Changes in conditions (e.g., concentration, temperature) affect reactions at equilibrium, following Le Chatelier’s Principle.

4.6.2.5 Changing Concentration Effects

• Altering reactant or product concentration shifts the equilibrium position until re-established.

4.6.2.6 Temperature Changes Effects

• Raising temperature favors endothermic reactions while lowering favors exothermic, affecting product levels.

4.6.2.7 Pressure Changes Effects

• In gaseous reactions, higher pressure shifts equilibrium towards the side with fewer molecules and vice versa.

4.7 Organic Chemistry

• The chemistry of carbon compounds, crucial for biological and industrial processes.

• Carbon’s ability to form diverse structures leads to many materials.

4.7.1 Carbon Compounds as Fuels and Feedstock

4.7.1.1 Crude Oil, Hydrocarbons, and Alkanes

• Crude oil is a finite resource from ancient biomass, primarily hydrocarbons.

• Alkanes have a general formula CnH2n+2; first four are methane, ethane, propane, butane.

4.7.1.2 Fractional Distillation and Petrochemicals

• Fractional distillation separates crude oil into fractions with similar carbon counts for various uses.

4.7.1.3 Properties of Hydrocarbons

• Properties depend on molecular size; includes boiling point, viscosity, and flammability.

• Complete combustion yields CO2 and H2O.

4.7.1.4 Cracking and Alkenes

• Cracking produces smaller hydrocarbons; methods include catalytic and steam cracking; useful for alkenes.

4.7.2 Reactions of Alkenes and Alcohols

4.7.2.1 Structure of Alkenes

• Alkenes, with a double bond (C=C), have the formula CnH2n.

4.7.2.2 Reactions of Alkenes

• Alkenes undergo combustion, addition with hydrogen, water, and halogens.

4.7.2.3 Alcohols

• Alcohols, containing –OH, include methanol, ethanol, propanol, butanol; undergo fermentation.

4.7.2.4 Carboxylic Acids

• Carboxylic acids contain the –COOH functional group; include methanoic and ethanoic acids.

4.7.3 Synthetic and Naturally Occurring Polymers

4.7.3.1 Addition Polymerisation

• Polymers formed from monomers such as alkenes by addition reactions.

4.7.3.2 Condensation Polymerisation

• Involves monomers with two functional groups, producing larger molecules while releasing small ones.

4.7.3.3 Amino Acids and Proteins

• Amino acids react to form polypeptides; proteins constructed from varied amino acid chains.

4.7.3.4 DNA and Naturally Occurring Polymers

• DNA encodes genetic info; consists of nucleotides forming a double helix.

4.8 Chemical Analysis

• Analysts develop qualitative tests for chemicals based on specific reactions.

4.8.1 Purity, Formulations, and Chromatography

4.8.1.1 Pure Substances

• Pure substances melt/boil at specific temperatures; used for identification.

4.8.1.2 Formulations

• Designed mixtures for specific purposes, e.g., fuels, medicines, cleaning agents.

4.8.1.3 Chromatography

• Separates mixtures; Rf values determine identification of components.

4.8.2 Identification of Common Gases

4.8.2.1 Hydrogen Test

• Burning splint produces a pop sound.

4.8.2.2 Oxygen Test

• Glowing splint relights.

4.8.2.3 Carbon Dioxide Test

• Limewater turns milky.

4.8.2.4 Chlorine Test

• Damp litmus turns white.

4.8.3 Identification of Ions

4.8.3.1 Flame Tests

• Specific colors for certain metal ions during testing.

4.8.3.2 Metal Hydroxides

• Precipitation reactions indicate presence of metal ions.

4.8.3.3 Carbonates

• React with acids to produce CO2.

4.8.3.4 Halides and Sulfates

• Precipitation methods to identify halides and sulfates.

4.9 Chemistry of the Atmosphere

4.9.1 Composition and Evolution

4.9.1.1 Gas Proportions

• Modern atmospheric gases: ~80% nitrogen, ~20% oxygen, minor gases (CO2, water vapor).

4.9.1.2 Early Atmosphere

• Early Earth atmosphere theory links volcanic activity, CO2, and lack of O2.

4.9.1.3 Oxygen Increase

• Photosynthesis by algae/plants resulted in atmospheric O2 increases.

4.9.1.4 Carbon Dioxide Decrease

• Carbonation processes reduced CO2 levels.

4.9.2 Greenhouse Gases

4.9.2.1 Greenhouse Effect

• Greenhouse gases maintain temperatures for life; interaction of radiation and matter.

4.9.2.2 Human Contributions

• Human activities elevate greenhouse gases, affecting global temperatures.

4.9.2.3 Climate Change

• Rising temperatures lead to various ecological challenges.

4.9.3 Atmospheric Pollutants

4.9.3.1 Sources and Effects

• Fuel combustion emits harmful pollutants; forecasting their effects is crucial for environmental health.

4.9.3.2 Properties of Pollutants

• Carbon monoxide is toxic; others cause respiratory issues, global dimming, and health complications.

4.10 Using Resources

4.10.1 Sustainable Development

4.10.1.1 Resource Utilization

• Resource management must meet present needs without compromising future resources.

4.10.1.2 Potable Water

• Safe drinking water treatment involves filtration and sterilization.

4.10.1.3 Waste Water Treatment

• Approaches for treating sewage and industrial waste are critical for environmental protection.

4.10.1.4 Alternative Metal Extraction

• Biological methods like phytomining reduce environmental impacts from traditional mining.

4.10.2 Life Cycle Assessment and Recycling

4.10.2.1 Life Cycle Assessment

• Evaluates environmental impacts through all product life stages; considers resource use and waste.

4.10.2.2 Resource Reduction

• Encouraging reuse and recycling minimizes resource depletion and waste.

4.10.3 Materials Science

4.10.3.1 Corrosion Prevention

• Methods like painting and galvanizing protect metals from corrosion, notably rust.

4.10.3.2 Alloys

• Alloys possess tailored properties for various applications; examples include bronze and stainless steel.

4.10.3.3 Ceramics, Polymers, and Composites

• Discuss properties and applications of glass, ceramics, polymers, and composite materials.