Combined Chemistry AQA

• Substances are made of atoms, which are represented in the periodic table by a symbol.
• A compound is a substance that contains two or more different types of atoms chemically bonded together, for example, the chemical formula for water is H2O, made up of hydrogen and oxygen atoms.
• For every one oxygen atom in a compound, there are two hydrogen atoms.
• Atoms change what they're bonded to and how they're bonded through chemical reactions.
• A reaction can be represented with a word equation and a chemical equation using symbols.
• There must be the same number of each type of atom on both sides of a chemical equation, so sometimes we must balance equations.
• A mixture is any combination of any different types of elements and compounds that aren't chemically bonded together, for example, air is a mixture of oxygen nitrogen and more.
• Solutions are mixtures that contain a solute dissolved in a solvent, for example, salt water is a solution of water and sodium chloride.
• Filtration, crystallization, evaporation, and distillation are physical processes used to separate the different liquids of a mixture as they have different boiling points, this is called fractional distillation.
• A mole is a specific number of atoms or molecules, used as a way of comparing amounts of substances.
• Total mass of all substances is conserved in a chemical reaction, meaning the atoms that go in must come out.
• Graphite is an allotrope of carbon made out of the same atoms bonded together in a different way, consisting of layers of carbons with three bonds each in a hexagonal structure.
• Relative formula mass (Rams) is calculated by adding up the individual Rams of a compound.
• Relative atomic mass (Rams) is a way of comparing amounts of substances as we can't deal in individual numbers of atoms or molecules.
• In a chemical reaction, the stochiometry is the ratio of moles of one substance to another.
• Nanoparticles are structures that are between 100 and 2,500 nanm in size.
• Simple molecular or simple calent structures are individual molecules that can all mix together and have relatively low boiling points due to weak intermolecular forces.
• Graphene is a single layer of graphite.
• Diamond is a crystal of carbon atoms bonded to each other, making it hard and with a high melting point.
• Solid, liquid, and gas are the three main states of matter, for example, water can be ice a solid where the particles or molecules vibrate around fixed positions, liquid water where the molecules are still touching but are free to move past each other, and water vapor when it's water where the particles are far apart and move randomly.
• Gases can be compressed while solids and liquid cannot.
• To melt or evaporate a substance, you must supply energy usually in the form of heat to overcome the electrostatic forces of attraction between the particles.
• JJ Thompson discovered that atoms are made up of positive and negative charges, leading to the plum pudding model of the atom.
• The more reactive ion stays in solution while the less reactive one moves to the electrodes.
• Chemical batteries contain chemicals that can produce a potential difference of voltage to power electrical appliances.
• If less energy is released than goes in, the reaction is endothermic, as seen in a fuel cell.
• If there is more energy released from bonds made than energy needed to break bonds, it is a net energy released and the reaction should increase in temperature.
• Any chemical reaction involves energy transfers as energy is needed to break chemical bonds and energy is released when chemical bonds form.
• An energy profile can be used to visualize the difference in energies between the reactants and the products.
• Hydrogen fuel cells work in a similar way to batteries, where water is split up into hydrogen and oxygen by electrolysis when they recombine a voltage is produced.
• If there is a halide ion present, it is oxidized at the anode.
• Sodium chloride solution is a mixture of Na+, Cl-, H+, and O- ions, which have partially dissociated.
• Non-renewable batteries stop working when the reactants are used up, while rechargeable batteries can be recharged when a supplied current causes the reverse reaction to occur.
• If there is no halide ion in solution, the oxygen from the O- ion is oxidized instead and oxygen gas is produced.
• If more energy is released than goes in, the reaction is exothermic, as seen in combustion.
• Hydrogen gas is made at the cathode in a sodium chloride solution if the metal is less reactive than hydrogen, such as in a copper sulfate solution.
• Fuel must need a spark to start it burning, which is why a bump is drawn to represent the activation energy.
• Ernest Rutherford found that the positive charge in the nucleus must be incredibly small, leading to the discovery of the nucleus.
• The mass of water is 18 that's 144 G of water.
• Atom economy tells you how much of a desired product you get out of a reaction compared to the mass of the reactants that went in.