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Chapter 10 Notes, part II. Balancing Chemical Equations. Reminder: The L aw of C onservation of Mass states that you can’t lose or gain matter when bonding. (This means that there is the same amount of matter after the reaction as there was before it started!). Vocabulary.
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Chapter 10 Notes, part II Balancing Chemical Equations
Reminder: The Law of Conservation of Mass states that you can’t lose or gain matter when bonding. (This means that there is the same amount of matter after the reaction as there was before it started!)
Vocabulary • Chemical Reaction:the act of changing substances into new substances with new and different chemical and physical properties. • Chemical Equation:describes the identities and relative amounts of the reactants and products involved in a chemical reaction.
2H2 + O2a 2H2O reactants The substances you have before a chemical reaction occurs (found on the leftside of the equation) products The substances you have after a chemical reaction occurs (found on the right side of the equation)
subscripts How many atoms of an element are in a compound “yields” a 2H2 + O2a2H2O 2H2 + O2a2H2O coefficients How many substances are in the reaction
Other Symbols in an Equation • (s) = substance is solid • (l) = substance is liquid • (g) = substance is a gas • (aq) = substance is dissolved in water • D = heat These are written after the compound and in parentheses.
Rules to remember: • To fix an inequality, you can ONLY use coefficients! • Subscripts stay the same — otherwise you are changing what chemicals you have. • Balance the inequalities for each element, then check to see if you have made anything else unequal and repeat.
Steps to Balancing Equations • Write the Skeleton Equation for the reaction. H2(g) + Cl2(g) → HCl(g) • Count the atoms of the elements in the reactants. H2(g) + Cl2(g) → 2 atoms H 2 atoms Cl
Steps to Balancing Equations 3. Count the atoms of the elements in the products. HCl(g) 1 atom H + 1 atom Cl 4. Change the coefficients to make the number of atoms of each element equal on both sides of the equation. H2(g) + Cl2(g) → 2HCl(g) 2 atoms H 2 atoms Cl2 atoms H + 2 atoms Cl
Steps to Balancing Equations • Helpful Hint: Count and balance metals first and then non-metals . Balance Hydrogen next and then Oxygen last. 5. Reduce the coefficients in their lowest possible ratio. 6. Check your work.
Mg + O2aMgO 2 + 1 a 2
Fe + O2a Fe2O3 4 + 3 a 2
Cu(OH)2aCuO + H2O balanced
HgOa Hg + O2 2 a 2 + 1
Fe + HCla FeCl2 + H2 1 + 2 a 1 + 1
C3H8 + O2a CO2 + H2O 1 + 5 a 3 + 4
Al + Pb(NO2)2a Al(NO2)3 + Pb 2 + 3 a 2 + 3
Mg(ClO3)2a MgCl2 + O2 1 a 1 + 3