Chemical Reaction Equations

1. Chemical Reaction Equations Writing & Balancing them… 11.1 Notes

2. the basic parts… • reactants: left side, starting materials • arrow: a chemical reaction has occurred • products: right side, ending materials • (l), (g), (s), (aq) - phase of the substance • aq = aqueous (dissolved in water) NOTE: in this phase, ions “dissociate” - come apart

3. word equations name of the compounds example: hydrogen gas and chlorine gas combine to form hydrogen chloride gas skeleton equations formulas example: H2(g) + Cl2(g) --> 2HCl (g) Writing Equations Don’t copy

4. Balancing Equations • Law of Conservation of Matter - matter is not created or destroyed • number of atoms for each element before and after the reaction must be equal. • Example: H2(g) + Cl2(g) --> 2HCl (g) • reactants: 2 H & 2 Cl • products 2 H & 2 Cl • the two sides are balanced!

5. Steps for balancing…. Don’t copy • Write the skeleton equation • Count atoms on each side of arrow (remember to look at the subscripts & the coefficients!) • Change coefficients so the atoms are balanced; NEVER change subscripts! • Make sure coefficients are in lowest ratio possible • Check your work!

6. Practice Problems • ___ ZnS (aq) + ___ O2 (g) --> ___ ZnO (aq) + ___ S (s) • ___ Cu + ___ AgNO3___ Ag + ___ Cu(NO3)2 • ___ H3PO4 + ___ NaOH ___ Na3PO4 + ___ H2O • ___ Ca3(PO4)2 + ___ H2SO4___ CaSO4 + ___ H3PO4 • Note: if the coefficient is “1” you don’t need to write anything.

7. More Practice… • ___ H2O + ___ CH4___ H2 + ___ CO2 • ___ Cl2 + ___ NaBr ___ NaCl + ___ Br2 • ___ Al(OH)3 + ___ H2SO4___ H2O + ___ Al2(SO4)3 • ___ C3H8 + ___ O2___ H2O + ___ CO2

8. Starting with words, then balancing • Aqueous iron (III) bromide reacts with chlorine gas to form iron (III) chloride and bromine gas. • Write the formulas in the skeleton equation • Then balance - DO NOT change the subscripts once you decide you have the formulas written correctly! • Solutions of barium hydroxide and sulfuric acid (H2SO4) react to yield water and solid barium sulfate.