Chemical Reactions

• Atoms consist of a positive nucleus containing protons and neutrons surrounded by electrons orbiting the nucleus.
• The mass of the atom is concentrated inside its nucleus and is the sum of the mass of the protons and neutrons.
• Elements are pure substances that contain the same type of atoms.
• A compound is a chemical substance made up of atoms of two or more elements held together in fixed ratios by chemical bonds.
• Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
• Covalent bond : a bond in which two non-metallic atoms share one or more pairs of electrons.
• Ionic bond: a bond in which some atoms gain and some lose electrons, becoming ions.
• Covalent compounds form between non-metal elements and form when the atoms share their valence electrons in order to complete their valency.
• Ionic Compounds form between a metal element and non-metal and form when positive ion bonds to a negative ion due to electrostatic forces.
• Polyatomic ion: two or more ions bonded together and acting as a single charged unit.
• Law of conservation of mass: mass cannot be created or destroyed.
• Reactant : a substance that starts a chemical reaction.
• Product : a substance formed in a chemical reaction.
• An acid is a corrosive chemical substance that produces hydrogen ions (W) when mixed with water.
• The higher the concentration of hydrogen ions produced by an acid, the higher its acidity.
• A base is a substance that reacts with an acid to neutralise it.
• Bases that dissolve in water are called alkalis.
• Three types of bases: (metal) hydroxide, oxide, carbonate.
• The acidity of a solution is measured on a scale called the pH scale.
• Acids have a low pH, while bases have a high pH.
• Litmus(indicator): turns red when acidic, turns blue when its a base.
• Chemical reaction: Any chemical change that occurs when two or more substances combine or separate to form a new substance.
• In a neutralisation reaction, an acid and a base react to form salt and water.
• Acids react with metals to form salt and hydrogen gas.
• A metal carbonate is a compound containing metal, carbon and oxygen.
• Acids react with metal carbonates to form salts, carbon dioxide and water.
• An oxidation reaction is a reaction that occurs in the presence of oxygen.
• Ex: combustion and corrosion.
• A combustion reaction takes place between a compound and oxygen to produce heat and a new product (oxide compounds).
• Ex: burning wood, respiration in cells (fast).
• Hydrocarbon : a compound made up of only hydrogen and carbon.
• Fuel +Oxygen >> carbon dioxide +water
• Precipitation reaction: two salt solutions are mixed, and two products are formed - an insoluble solid and a soluble salt.
• Respiration: the process of using glucose to obtain energy, a type of combustion reaction
• Concentration increase rate of reaction as more collisions occur if there are more particles
• Enzymes are biological catalysts that speed up the rate of chemical reactions and reduce the amount of energy needed to start a reaction.
• Types of enzymes include carbohydrate, lipases, proteases
• Surface area: the area of the outermost layer of an object
• Exothermic: a reaction that releases energy in the form of heat (-light) Reactants have more energy than products
• Catalysts are specific, which means that each catalyst increases the rate of some reactions but not others