MATSEC SEC Chemistry flashcards
MATSEC SEC Chemistry · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Mole
- The amount of substance containing 6.02 × 10²³ particles (Avogadro constant). One mole of any gas occupies 22.4 dm³ at s.t.p. and its mass in grams equals its relative formula mass.
- Avogadro constant
- The number of particles in one mole, 6.02 × 10²³ mol⁻¹. Multiply moles by this value to find the number of atoms, ions or molecules in a sample.
- Empirical formula
- The simplest whole-number ratio of atoms of each element in a compound. Found by dividing each element's mass or percentage by its atomic mass, then by the smallest result.
- Relative atomic mass
- The weighted mean mass of the naturally occurring isotopes of an element, compared with one-twelfth the mass of a carbon-12 atom. It is not a whole number for most elements.
- Isotopes
- Atoms of the same element with the same number of protons but different numbers of neutrons. They have identical chemical properties but slightly different masses and physical behaviour.
- Ionic bonding
- Electrostatic attraction between oppositely charged ions formed when a metal transfers electrons to a non-metal. The giant lattice gives high melting points and conducts only when molten or aqueous.
- Covalent bonding
- A shared pair of electrons between two non-metal atoms. Simple molecular substances have weak forces between molecules, so they melt easily and do not conduct electricity.
- Giant covalent structure
- A three-dimensional network of covalently bonded atoms, as in diamond and silicon dioxide. Very high melting points; graphite is an exception that conducts because of delocalised electrons between layers.
- Metallic bonding
- A lattice of positive metal ions surrounded by a sea of delocalised electrons. The mobile electrons explain electrical and thermal conductivity, while the layers explain malleability and ductility.
- Electrolysis
- The decomposition of an ionic compound by passing direct current through it when molten or in aqueous solution. Positive ions go to the cathode and negative ions to the anode.
- Group 1 reactivity trend
- Reactivity increases down Group 1 because the outer electron is further from the nucleus and more shielded, so it is lost more easily. Lithium reacts least vigorously; potassium most of the three.
- Halogen displacement
- A more reactive halogen displaces a less reactive halide from its solution. Chlorine turns potassium bromide solution orange, showing chlorine is more reactive than bromine.
- Noble gases
- Group 0 elements with full outer electron shells, so they are monatomic and chemically unreactive. Boiling points increase down the group as intermolecular forces become stronger.
- Transition metals
- Metals between Groups 2 and 3 with typical properties: variable oxidation states, coloured compounds, catalytic activity and high density. Iron and copper are common examples.
- Exothermic reaction
- A reaction that releases heat to the surroundings, giving a negative ΔH. Products are at lower energy than reactants, for example combustion and neutralisation.
- Activation energy
- The minimum energy colliding particles need before a reaction can occur. Catalysts lower it by providing an alternative reaction pathway, increasing the rate without being used up.
- Le Chatelier's principle
- When a system at equilibrium is disturbed by a change in concentration, pressure or temperature, it shifts in the direction that opposes the change. Catalysts do not affect the position of equilibrium.
- Haber process
- The industrial manufacture of ammonia from nitrogen and hydrogen using an iron catalyst at about 450 °C and 200 atm. High pressure favours ammonia; moderate temperature balances yield and rate.
- Homologous series
- A family of organic compounds with the same general formula and functional group, showing similar chemical properties and a gradual change in physical properties down the series.
- Alkane substitution
- Alkanes react with halogens in ultraviolet light by free-radical substitution, replacing a hydrogen atom. For example, methane and chlorine give chloromethane and hydrogen chloride.
- Alkene addition
- Alkenes are unsaturated and undergo addition reactions across the carbon–carbon double bond. Bromine water is decolourised, which is the standard test for an alkene.
- Fermentation of glucose
- Yeast converts glucose to ethanol and carbon dioxide anaerobically at about 30 °C. The ethanol is concentrated by fractional distillation; the process is used in the drinks industry.
- Esterification
- A carboxylic acid reacts with an alcohol in the presence of concentrated sulfuric acid to form an ester and water. Esters are volatile and have characteristic sweet fruity smells.
- Addition polymerisation
- Many unsaturated monomer molecules join to form a long saturated chain with no other product. Ethene monomers give poly(ethene), used for bags and bottles.
- Structural isomerism
- Compounds with the same molecular formula but different arrangements of atoms, giving different physical and sometimes chemical properties. Butane and 2-methylpropane are examples.
- Reactivity series
- A ranking of metals by how readily they lose electrons: potassium, sodium, calcium, magnesium, aluminium, zinc, iron, lead, copper, silver, gold. Metals above hydrogen displace it from acids.
- Blast furnace
- Iron is extracted from haematite by reduction with carbon monoxide at high temperature. Limestone removes the silica impurity as calcium silicate slag.
- Rusting conditions
- Iron rusts when both oxygen and water are present. Painting, greasing or galvanising excludes one of these, and sacrificial metals such as zinc corrode in preference to iron.
- Fractional distillation of crude oil
- Crude oil is heated and separated into fractions by boiling point in a fractionating column. Smaller molecules rise higher because they have lower boiling points.
- Acid rain formation
- Sulfur dioxide from burning fossil fuels and nitrogen oxides from engines dissolve in rainwater to form sulfurous, sulfuric and nitric acids. These corrode buildings and acidify lakes and soils.
- Titration end-point
- The point at which the indicator changes colour permanently, ideally matching the equivalence point. Concordant titres within 0.10 cm³ are averaged to calculate the unknown concentration.
- Chromatography R_f value
- The ratio of the distance travelled by a spot to the distance travelled by the solvent front. Each pure substance has a characteristic value under fixed conditions, allowing identification.