Presentation on theme: "Writing Chemical Equations"— Presentation transcript:
1 Writing Chemical Equations From Words to Numbers
2 IntroductionChemical change is represented by an equation in which the formulas for reacting substances (reactants) are written to the left. An arrow separates these from the formulas for products.2Al(s) + 3Br2(l) → 2 AlBr3(s)
3 Introduction (continued) 2Al(s) + 3Br2(l) → 2 AlBr3The physical state of each substance can be indicated by using (s) for solid, (l) for liquid, (g) for gas, and (aq) for an aqueous solution.
4 Introduction (continued) 2Al(s) + 3Br2(l) → 2AlBr3(s)The coefficients can be interpreted in terms of:Individual species2 Al atoms react with 3 Br2 moleculesAmounts in moles of species2 moles of Al react with
5 Introduction (continued) Chemical change does not result in destruction or creation of atoms. Thus all atoms in the reactants must also be present in the products.2Al(s) + 3Br2(l) → 2AlBr3(s)In the above equation there are 2 Al atoms and 6 Br atoms, thus matter is conserved.
6 Step 1 Identify all substances in the given problem Write their chemical symbols and/or formulasPay attention to your charges!!This means use subscripts but do not use coefficients at this point
7 Step 1 - ExampleThe reaction of zinc with aqueous hydrochloric acid produces a solution of zinc chloride and hydrogen gas.Zn(s)HCl(aq)ZnCl2(aq)H2(g)
8 Step 2 Determine the sequence of events in the reaction Identify the reactants and productsSet them up with an arrow going from reactants to products