Groups in the Periodic Table / Rates of Reaction / Heat Energy Changes in Chemical Reactions

Groups in the Periodic Table / SC18 Rates of Reaction / SC19 Heat Energy Changes in Chemical Reactions

Alkali Metals

Group 1 metals, reactive, soft, low density, react with water to form alkaline solutions and hydrogen gas

Halogens

Group 7 non-metals, form salts with metals, diatomic, highly reactive, reactivity decreases down the group

Noble Gases

Group 0, inert, full outer electron shell, unreactive, used in lighting and welding

Reactivity Trend

How easily elements react, increases down Group 1, decreases down Group 7, related to ease of electron loss/gain

Displacement

More reactive element replaces less reactive one in compound, evidence for reactivity series

Ionic Equations

Show only reacting ions in a reaction, spectator ions omitted, used to represent redox reactions

Redox

Reactions involving both oxidation (loss of electrons) and reduction (gain of electrons), occur simultaneously

Rates of Reaction

Speed at which reactants change to products, measured by change in concentration/mass/volume over time

Activation Energy

Minimum energy for reaction to occur, needed to break bonds

Catalyst

Substance that speeds up reaction without being changed itself, provides alternative reaction pathway with lower activation energy

Reversible Reactions

Reactions that can go forwards or backwards, represented by ⇌ symbol

Dynamic Equilibrium

Forward and reverse reactions occur at the same rate, concentrations of reactants and products remain constant

Le Chatelier's Principle

If conditions change, equilibrium shifts to counteract the change, affecting yield of products

Exothermic

Reaction that releases heat energy, ΔH is negative, temperature of surroundings increases

Endothermic

Reaction that absorbs heat energy, ΔH is positive, temperature of surroundings decreases

Enthalpy Change

Heat energy change in a reaction at constant pressure, measured in kJ/mol

Bond Energy

Energy needed to break a chemical bond, stronger bonds have higher bond energies

Hess's Law

Total enthalpy change is independent of the pathway taken, allows calculation of enthalpy changes

Calorimetry

Experimental measurement of enthalpy changes, using specific heat capacity and temperature change

Rate of Reaction

Change in concentration of reactant/product per unit time, units are mol/dm3/s

Maxwell-Boltzmann Distribution

Shows spread of energies of molecules in a gas, area under curve represents total number of molecules

Factors Affecting Rate

Temperature, concentration, surface area, pressure (for gases), catalyst, affect frequency of successful collisions

Order of Reaction

How concentration affects rate (e.g. first order means rate is proportional to concentration), determined experimentally

Rate Constant

Constant that links rate of reaction to concentrations of reactants, units depend on overall order of reaction

Half-life

Time taken for concentration of reactant to halve, used to determine order of reaction

Rate-determining Step

Slowest step in a reaction, determines overall rate of reaction

Acids

Proton donors, form H+ ions in water, pH < 7, neutralize bases

Bases

Proton acceptors, neutralize acids, pH > 7, soluble bases are called alkalis

pH Scale

Measures acidity/alkalinity, 0-7 acidic, 7 neutral, 7-14 alkaline, measured using universal indicator or pH meter

Neutralization

Reaction between acid and base, forms salt and water, exothermic reaction

Titration

Technique to find concentration of a solution using another solution of known concentration, uses burette and indicator

Electrolysis

Using electricity to split up ionic compounds, ions are discharged at electrodes

Electrolytic Cell

Apparatus for electrolysis, includes electrodes and electrolyte

Anode

Positive electrode, oxidation occurs at anode

Cathode

Negative electrode, reduction occurs at cathode

Oxidation

Loss of electrons, occurs at anode

Reduction

Gain of electrons, occurs at cathode

Ions

Charged particles, move during electrolysis, positive ions move to cathode, negative ions move to anode

Electrolyte

Solution that conducts electricity due to ions, contains mobile ions

Precipitation

Formation of a solid from two solutions, occurs when ions combine to form an insoluble compound

Hard Water

Water containing dissolved calcium or magnesium ions, forms scum with soap

Temporary Hardness

Caused by hydrogencarbonate ions, removed by boiling

Permanent Hardness

Caused by sulfate ions, not removed by boiling

Water Treatment

Filtration, chlorination to purify water, removes solids and microorganisms

Distillation

Separating liquids based on boiling points, used to purify water

Fractional Distillation

Separating mixture of liquids with close boiling points, used to separate crude oil

Crude Oil

Mixture of hydrocarbons, separated by fractional distillation

Alkanes

Saturated hydrocarbons, C-C single bonds, general formula CnH2n+2

Alkenes

Unsaturated hydrocarbons, C=C double bonds, general formula CnH2n

Isomers

Molecules with same formula but different structures, different properties

Cracking

Breaking long hydrocarbons into shorter ones using heat and catalysts, produces alkanes and alkenes

Reforming

Rearranging atoms in hydrocarbons to make branched chains and rings, increases octane number

Addition Polymerization

Joining monomers with C=C bonds to form long chains, forms polymers like polyethene

Condensation Polymerization

Monomers react, eliminate small molecule, form polymer, forms polymers like nylon and polyester

Polyesters

Condensation polymers with ester linkages, used in clothing and bottles

Polyamides

Condensation polymers with amide linkages, used in nylon and Kevlar

Amino Acids

Building blocks of proteins, contain carboxyl and amino groups

Proteins

Polymers of amino acids, have complex 3D structures

DNA

Contains genetic information, double helix structure, made of nucleotides

Polymers

Long chain molecules made of repeating units (monomers), have different properties depending on structure

Nanotechnology

Manipulating materials at the atomic/molecular scale, creates nanoparticles

Nanoparticles

Tiny particles with unique properties due to high surface area to volume ratio, used in sunscreens and catalysts

Fullerenes

Spherical carbon structures, used for drug delivery, lubricants

Carbon Nanotubes

Cylindrical carbon structures, strong, used in composites

Graphene

Single layer of carbon atoms, strong, conductive, used in electronic