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Unit 7: Chemical Reactions
Writing word and skeletal equations
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Chemical Reactions: When the atoms of one or more substances are rearranged to form different substances. CH O ⇒ CO H2O Reactants: Starting substances Products: Ending Substances
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Chemical Reaction Symbols: Write these in your flipbook
+ Separates two or more reactants or products ⇒ Separates reactants from products ↔ Separates reactants from products and indicates a reversible reaction (s) Identifies a solid state (l) Identifies a liquid state (g) Identifies a gaseous state (aq) Identifies a water solution (Aqueous)
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Law of the Conservation of Mass
Mass is neither created nor destroyed during a chemical reaction
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Signs of a chemical change:
Energy change Color change Odor change Production of gas Formation of a solid (precipitate)
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Key words for chemical reactions:
Reacts: tells us what is reacting with what We use a + to represent reacts/reacts with Yields/To form: tells us what the product(s) is We use an to represent yields/produces/to form * We state the state of the matter for each substance. (solid, liquid, gas, or aqueous)
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Change in Energy Energy either being gained or released as heat or light Two types: Exothermic: Energy released by the reaction We will see light or feel heat Endothermic: Energy gained by the reaction We will feel the reaction getting cold
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Odor Change: Color Change: Production of a gas:
Rotting, baking, cooking, etc. Color Change: Typically associated with another sign of a chemical change The formation of a solid/percipitate Note: Mixing of colors, diluting, etc, are not signs of a chemical change Production of a gas: Formation of bubbles, etc This is not caused by heating or boiling a substance.
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Formation of a Solid: A solid is formed during the reaction, when adding or taking away energy from the rxn. This solid is known as a precipitate. It is NOT mean the freezing of a liquid into a solid.
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Word Equations: Chemical Rxn in word format:
Solid Aluminum and liquid bromine react to produce solid aluminum bromide.
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Skeletal Equations Chemical reactions using chemical symbols/formulas and chemical reaction signs. Written from a word equation: Solid Aluminum reacts with liquid bromine to form solid aluminum bromide. Al(s) + Br2(l) AlBr3(s)
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Key Words: Remember the key words give us information about the reaction
Carbon monoxide gas and oxygen gas react to yield carbon dioxide gas. CO(g) + O2(g) CO2(g)
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States of Matter: (write these in your flipbook)
Solid (s) Liquid (l) Gas (g) Aqueous (aq)
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Diatomic Elements: CO(g) + O2(g) CO2(g) Al(s) + Br2(l) AlBr3(s)
Notice that some of the elements have a 2 after them in their skeletal equations: These are called diatomics: These are elements that cannot exist in nature a single atom. If they are NOT in a compound, then they must be bonded to another atom of the same element Cl + Cl = Cl2 CO(g) + O2(g) CO2(g) Al(s) + Br2(l) AlBr3(s)
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Diatomic Elements: Check and make sure these are correct in your flipbook
There are 7 diatomics:
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Practice Problems: I will complete the first one with you, then you will try the rest on your own. You may write these right on your table, IF and ONLY IF you have a neon expo marker, if not please complete them on a separate sheet of paper.
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Practice: Aqueous Sodium hydroxide reacts with aqueous calcium bromide to form aqueous sodium bromide and solid calcium hydroxide.
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Practice: Solid zinc reacts with aqueous sulfuric acid to form hydrogen gas and solid zinc (II) sulfate. Solid barium hydroxide decomposes into solid barium oxide and water.
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