20F Chemistry Review Part 2 +

reactants products 2 + A + 2 B C Chemical reaction – substances react to produce one or more new substances. Chemical equation – contains all necessary information about a reaction. 2 + reactants products A + 2 B C

(l) = liquid (g) = gas (s) = solid *(aq) = aqueous At this level it is expect that you can decipher chemical reactions as word equations: Hydrogen gas and oxygen gas react to form water vapour H + O H2O 2 (g) 2 (g) (g) diatomic State (phase) of the substance is always shown as small subscripts after the compound formula: (l) = liquid (g) = gas (s) = solid *(aq) = aqueous *Aqueous means this compound has dissolved in water

H2 (g) + O2 (g) H2O (g) 2 2 The Law of Conservation of Mass (balancing equations): In any chemical reaction matter cannot be created or destroyed. H2 (g) + O2 (g) H2O (g) 2 2 H H O H H O O H H H H O was This equation is unbalanced because the atoms are not conserved from one side (reactants) to the other (products)

Rules for Balancing Equations Coefficients (phase/state) Subscripts H2 (g) + 1O2 (g) H2O (g) 2 2 Coefficients indicate the ratio of the substances in the chemical reaction. “Two molecules of hydrogen react with one molecule of oxygen to yield two molecules of water.” Coefficients of 1 are not typically written Rules for Balancing Equations You cannot change the formula of any reactant or product. 2. You can only change the coefficients in front of the reactants and products.

2 HCl + MgBr2 MgCl2 + HBr 2 Balanced H: 1 H: 1 (2) = 2 (2) = 2 Cl: 1 Cl: 2 Mg: 1 Mg: 1 Br: 2 Br: 1 (2) = 2 (2) = 2 (2) = 2 (2) = 2 Balancing Tips: Find a way to track it that is meaningful to YOU. Balance metals first, then non-metals. Balance single elements last. Check and recount all the atoms. Prepare for trial and error.

CH4 + O2 CO2 + H2O 2 2 Balanced C: 1 C: 1 H: 4 H: 2 O: 2 O: 2 + 1 (2) = 4 (2) = 4 (2) = 4 We want to get to a place where this work happens in our head with minimal notation work Balancing Tips: Find a way to track it that is meaningful to YOU. Balance metals first, then non-metals. Balance single elements last. Check and recount all the atoms. Prepare for trial and error.

Anything that has mass and takes up space, or volume. Matter: Anything that has mass and takes up space, or volume. Na NaCl NaCl + H2O NaCl + Pepper

A “staircase” on every Periodic Table separates the metals from the non-metals (with metalloids in between)

Can be qualitative or quantitative Physical properties Testing or measuring these traits will NOT change the original composition (what it is made of) Can be qualitative or quantitative quality quantity State/phase – solid, liquid or gas (at room temperature) Hardness – how easy it is to scratch or dent Viscosity – how easy it flows Melting point – unique temperature needed to change from solid into liquid Boiling point – unique temperature needed to change from liquid into gas

Other examples of Physical Properties: Lustre – shiny (opposite – dull) Malleability – how easy to bend or flatten (opposite – brittle) Ductility – how easy to pull into a wire Solubility – how well it dissolves in water Conductivity – how well it transfers heat/electricity Quantitative traits require a measurement – melting point Qualitative traits don’t need one – state

Anything that changes what it “looks like” NOT “what it is” Physical Change A change in shape or state of a substance - crushing, cutting, folding, smashing, melting, boiling… No evidence of a new material forming H O Anything that changes what it “looks like” NOT “what it is”

Trait describes if substance reacts chemically Chemical properties Trait describes if substance reacts chemically Testing or measuring these traits WILL change the original composition (will create something new) Reactivity – does it react quickly? Combustibility – does it ignite or burn? Corrosion – does it react with acids? Oxidation – does it react with air? Toxicity – does it react with the body? Testing a chemical property requires a chemical reaction that will alter what you test: wood  ash

A chemical reaction has happened! Chemical change A change in the properties of a substance **Means a new substance is formed A chemical reaction has happened! Evidence of a chemical change (and chemical reaction): A change in colour A change in smell 3. Fizzing or bubbling (new gas being made)

This new solid is called a precipitate 4. A new solid forms from a mixture of liquids or the mixture goes cloudy This new solid is called a precipitate A change in energy Exothermic: energy is released (product) Endothermic: energy is absorbed (reactant) “Energy” could be light, heat, sound – think of the most obvious change in energy reaction – an EXPLOSION!

Testing the property can cause a… Physical properties Chemical properties Testing the property can cause a… Physical change Chemical change Δ colour Δ smell Δ energy Gas bubbles Precipitate State or shape NO Reaction Chemical Reaction Same substance with same properties New substance with new properties