Describe how atoms are rearranged during a chemical change
When the reactants come into contact, if the energy equal to or more than the activation energy, the bonds break. With the bonds broken, the atoms are free to move. The free atoms form new chemical bonds with each other. The new arrangement of atoms are the new products.
Describing observations in a chemical reaction in word equations
Colour change
Formation of new solid (precipitate)
Production of gas (bubbles, odour)
Temperature change (heat absorbed and released)
Emission of light
Or changes in a substance’s smell, state or magnetism and the irreversibility
Write word and symbol equations for acid + base
Neutralisation Reactions (acids and bases neutralise each other)
Acid + base -> salt + water
Write word and symbol equations for the acid + carbonate
Acid + carbonate -> salt + water + carbon dioxide
Write word and symbol equations for acid + reactive metal.
Acid & Metal (acids can corrode metal)
Acid + metal -> salt + hydrogen gas
Law of Conservation of Mass
Mass is neither created nor destroyed in a chemical reaction
Role of oxygen in combustion
Acts as oxidising agent, reacting with fuel to create a combustion reaction
Compare combustion with other oxidation reactions
Combustion is rapid, produces significant amounts of heat/light and is often uncontrolled. Other oxidation reactions are slower more controlled and don’t always release light. An example is corrosion
Combustion
A chemical reaction where fuel reacts with oxygen to release energy (heat and light)
Fuel
A substance that burns, releasing energy.
Examples: wood, diesel, coal, natural gas
Combustion
A chemical reaction where fuel reacts with oxygen to release energy (heat and light). Combustion is an exothermic reaction. It releases heat energy into its surroundings.
Word and symbol equation for combustion reactions
Fuel + Oxygen → carbon dioxide + water + energy
Fuel + O2 → CO2 + H20 + heat
Where does combustion occur in everyday life?
Lighting a fire, bunsen bumer, diesel engine cars
Corrosion
Metal + oxygen → meta oxide + energy
Metal atoms lose elections and become oxidised. Oxygen atoms gain these elections, undergoing reduction. The oxidised metal and reduced oxygen combine to form a new substance, a metal oxide
Conditions that support rusting
- presence of salts (eg. seawater)
- high humidity
- water (needed)
- impurities of iron/other substances (eg. acids, carbon dioxide)
Rusting word and symbol equations
Iron + water + oxygen → hydrated Iron (III) Oxide
4Fe + 3O2 + 6H20 → 4Fe(OH) 3
Methods to prevent to rusting
Painting, coating or oiling - applying dry coating creates physical barrier that presents moisture and oxygen tron reching metal surface. By blocking these elements, the reaction cannot happen.
Galvanisation - coating metal in layer of zinc. zine is more electronical reactive than iron of steel. it will corrode itself befor iron does
System
A collection of interacting or interrelated components that form a unified whole, working together to perform function
Surrounding
All around a particular place or thing
Chemical energy
Energy stored within bonds of atoms and molecules that can be released during a chemical reaction, often as heat or electricity
Endothermic
Reaction that absorbs heat. Object gets hotter, surroundings get colder
Exothermic
Reaction that releases heat. Object gets colder, surroundings get hotter.
Role of energy in chemical reactions
Energy breaks bonds in reactants and forms new bonds in products
Explain the role of bond breaking and formation in a physical and chemical change and how they relate to energy change during a reaction
In a physical change, bonds do not break or form. Instead, intermolecular forces are disrupted, allowing the substance to chang torm. In a chemical reaction, bonds break in the reactants and bonds form in the products, making new molecules. Energy change is the process where energy is either absorbed from or released into the surroundings. It can be endothermic (absorbing from surroundings) or exothermic (releasing into suroundings). Bond breaking always requires energy (is endothermic), while bond formation alway releases energy (is exothermic).
