6A word equationMagnesium metal reacts with oxygen gas to form white magnesium oxide solid.We must learn how to translate these!
7Balancing equations Tips __Fe2O3 + __H2SO4 __Fe2(SO4)3 + __H2OIf possible treat polyatomic ions as 1 unitBalance hydrogen 2nd lastBalance oxygen lastIf the last element does not balance double everything
8Ways to Represent Reactions Chemical equation: symbols that describe a chemical reaction and show what atoms (and how many, relatively speaking) are involved.Word equation: the names of each product/reactant are written out. Doesn’t show how many of each
9Write out the word equation Magnesium metal reacts with oxygen gas to form magnesium oxide solid.Mg + O MgO
10Remember BrINClOFH Br2 – a liquid I2 - a solid N2 - a gas Cl2 - a gas O2 - a gasF2 - a gasH2 - a gas
11Check for BrINClOFHAny time you see 1 of the 7 diatomic elements alone, write them with a 2 subscriptMg + O2 MgO
12Balance the charges of ionic comp In our reaction we have already done this, but make sure to use proper formulas (for molecular comp too!):MgO = Mg2+ O2-Mg + O2 MgO
13Balance number of atoms/ions on each side In ordinary chemical changes, atoms just rearrangeThis is the LAW OF CONSERVATION OF MATTERWe do this with coefficients2Mg O2 2MgO
14ExampleIf you take Ca(NO3)2 and change it to 2Ca(NO3)2, how many of each element do you have?
15Put in physical states Symbols used in chemical equations: (s) solid (l) liquid(g) gas(aq) aqueous solution (dissolved in H2O)
16Put in physical statesI will give you physical states in word problems:Magnesium metal reacts with oxygen gas to form magnesium oxide solid2Mg(s) O2(g) 2MgO(s)
17Word Equation exampleHydrogen gas and Oxygen gas combine to form liquid water.2H2(g) + O2(g) 2H2O(l)
18Example:Sodium solid reacts with chlorine gas to form sodium chloride solid.2Na(s) + Cl2(g) 2NaCl(s)
19Try this one:Dicarbon dihydride reacts with oxygen gas to produce carbon dioxide gas and water
20Evidence of rxns All rxns involve chemical change Look for evidence of those changes:Light, heat, gas, color change, precipitate
21Other Symbols precipitate forms gas forms “produces” or “yields” products can reform in to reactants – end result is a mix of the two.Δ – means that heat was added
23Experiment 17 Please read over steps 1-8 carefully Get the proper safety gear, and the proper equipmentDo steps 1-8, then set the solid aside to dry (step 9)Return to your seat – while the solid dries, you can work on A7At the end of class – record the mass of your beaker and solid.
24Balanced equations show RATIOS The coefficients of a balanced equation reveal the RATIO of each reactant to each product:2H2 + O2 2H2O means there is a 2:1:2 ratio of H2 to O2 to H2O.This is the same as a 4:2:4 ratio, etc. etc.
25The activity seriesWriting an equation doesn’t mean it will actually happenHow do we know it will happen?Single replacement reactions are predicted with the activity seriesThis activity series has been created through experiment.
26The activity seriesThings on the list will displace anything below but not above other things on the listThere are two lists – one for elements that become positive ions, and one for elements that become negative ions.
27ElementReactivityLi Rb K Ba Ca NaReact with cold H2O and acids, replacing hydrogenF2 Cl2 Br2I2Listed from most reactive to least reactiveMg Al Mn Zn Cr FeReact with acids or steam but usually not liquid water, to replace hydrogenNi Sn PbAll react with acids but not water, to replace hydrogenH2 Cu HgAll react with oxygen to form oxidesAg Pt AuMostly unreactive
28? When a rxn releases energy, where does it come from? You have to put energy in to break bondsIf bonding is stronger in the products they will be more stableMore stable = lower energyLower energy means energy must be RELEASEDThis is an exothermic reactionIs this an example of an ENDOthermic or EXOthermic reaction?
29If bonding is weaker in the products, they will be less stable, have more energy, and will therefore absorb it.Is this an endo or exothermic rxn?