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Mastering Chemical Equations: Rules and Balancing Examples

Learn to write chemical equations, balance them, and interpret word problems. Understand key elements, ions, and symbols. Improve your chemistry skills today!

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Mastering Chemical Equations: Rules and Balancing Examples

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  1. Chemical Equations

  2. Things you should already know… • Elements from the periodic table • Your polyatomic ions • The BrINClHOF’s • How to write ionic and covalent compounds names • The symbols for solid, liquid, gas, and aqueous • How to interpret word problems

  3. Other Things to Know • When metals are just named (i.e. Lead) this is simply the solid pure element ( i.e. Pb(s)) • When you are told something is “bubbled in” that means a gas form of that element is being added • Ex. “hydrogen is bubbled into a solution of…” • Is written as: H2(g) + …  …

  4. More Things You Should Know • Solutions are all aqueous (aq) • Ex: “a solutions of lead (II) chloride…” • PbCl2 (aq) • Acids are all aqueous

  5. Rules for Writing Chemical Equations • Figure out which are reactants and which are products. • Write chemical formulas for all substances, separated by the  • Add state of matter to each substance • Balance equation

  6. Chemical Equations Examples • Zinc and aqueous lead(II)nitrate are combined in an aqueous solution to produce zinc nitrate and a lead precipitate. • zinc and lead(II)nitrate are reactants; zinc nitrate and lead are products • Zn + Pb(NO3)2 Zn(NO3)2 + Pb • Zn(s) + Pb(NO3)2(aq) Zn(NO3)2(aq) + Pb(s) • Balance: coming right up!

  7. Chemical Equation Examples • Carbon tetrachloride may be prepared by the reaction of natural gas, methane, and chlorine in the presence of ultraviolet light. Hydrochloric acid (HCl) is also a product of this reaction. • methane and chlorine are the reactants; carbon tetrachloride and hydrochloric acid are the products • CH4 + Cl2 CCl4 + HCl • CH4(g) + Cl2(g)  CCl4(s) + HCl(aq) • To Balance

  8. Balancing Chemical Equations • Big Idea: Law of Conservation of Matter • Matter cannot be created or destroyed • Number of atoms of a certain element must be equal on reactant and product side. • A balanced chemical equation shows the ratio of elements from one side to other

  9. Rules for Balancing Equations • Write unbalanced equation • Once unbalanced equation is written, NEVER CHANGE THE SUBSCRIPTS • Only add coefficients to front of compound • Coefficients multiply everything in the compound by that amount • Work with most complex molecule first, and save simplest for last • If you have an odd # of elements on one side, multiply entire eqn by 2, and continue

  10. Review: Reading Molecular Numbers How many oxygen atoms? 2 1 4 8 4 24 • O2 • H2O • PO43- • 2H2SO4 • 2Ca(OH)2 • 3Ca3(PO4)2

  11. Balancing Examples • O3 O2 • You need the same number of O’s on both sides • 2O3  3O2 • 6 = 6 • Balance: H2 + O2  H2O • 2H2 + O2  2H2O • H’s : 4 O’s : 2

  12. Relating to Types Chemical Reactions • Combustion of ethane • C2H6 + O2 CO2 + H2O • Which is most complex? • Ethane – so balance those elements first • C2H6 + O2 2CO2 + 3H2O • Now you have odd number of O’s • Multiply entire eqn by 2 • 2C2H6 + O2 2CO2 + 3H2O • 2C2H6 + 2O2 4CO2 + 6H2O • Balance O’s • 2C2H6 + 7O2 4CO2 + 6H2O • Make a T chart to double check balance of all elements on both sides

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