Chemical equations show …The reactants and the products Reactants Products
Chemical equations show …The physical states of the reactants and products:(s) = solid (l) = liquid (g) = gas(aq) = aqueous solution HCl(g) + NH3(g) NH4Cl(s)
Chemical equations show …• The progress of a reaction … The shows progress from left to right. A double arrow shows an equilibrium between reactants and products.
Chemical equations show …• The presence of a catalyst A catalyst is a substance that appears not to take part in a reaction, but causes the reaction to go faster. The catalyst is written Pt above the arrow.
Chemical equations show …• Heat is added to the reaction. Added heat is indicated by the Greek letter delta ( ∆ ) The delta is placed ∆ over the arrow
Coefficients• The coefficients show the number of molecules or atoms of each reactant and product.• The coefficients are written in front of the symbols• The coefficients allow us to balance the equation.
Why balance an equation?A balanced equation adheres to the Law of conservation of mass “Matter is neither created, nor destroyed, only changed in form.”We must account for every atom that undergoes a reaction.
Balancing EquationsExample: balance the reaction of hydrogen and oxygen to make water: H2(g) + O2(g) H2O(l)
Balancing Equations• Make a table under the equation to The equation is kind of indicate the number of each balanced! atom as you change coefficients. 2 H2(g) + O2(g) 2 2O(l) H H 2 4 H 2 4 O 2 2 O 1 2
We will balance these together:1. Mn(s) + Cl2(g) MnCl4(S)2. Al2(SO4)3 Al2O3 + SO3(g)3. S(s) + O2(g) SO3(g)4. Na2CrO4(aq) + Fe(NO3)3 Fe2(CrO4)3(s) + NaNO3(aq)
Balance the Following Equations1. N2(g) + H2(g) NH3(g)2. Fe(s) + O2(g) Fe2O3(s)3. NaHCO3(s) Na2O(s) + H2O(g) + CO2(g)4. Ba(NO3)2(aq) + Na2SO4(aq) NaNO (aq) + BaSO (s)
“Word Equations”A balanced equation can be written from anexpression that describes a chemical reaction in words, rather than symbols.
To write a balanced equation…1. Determine the reactants and products. Look for clues: “added”, “produces”, “heated”, “decomposes”2. Write the correct formulas and put in the state symbols and any other symbols (I.e. catalyst or ∆).3. Balance the equation.
Consider the following:Propane gas (C3H8) burns in air to produce carbon dioxide gas and water vapor.Identify the reactants and products. Look for the clue. … to produce …
If something burns in air, what does it react with? OxygenWhat are the reactants? Propane and oxygenWhat are the products? Carbon dioxide and water
Write the formulas and symbols: Now balance the equation:C3H8(g) + 5O2(g) CO2(g) + H2O(g) 3 4