Stoichiometry

What is stoichiometry? Study of quantitative relationships in balanced chemical equation Chemical Equations represent chemical reactions

Physical vs. Chemical Change Physical Change = Chemical Change = Change in form or appearance Examples: Dissolving & phase changes Change in identity (formula) Example: Na(s) + Cl2(g) → NaCl(s)

Evidence of a Chemical Reaction Temperature change increase or decrease Emission of Light Energy Change in identifying property: - such as color, texture Formation of a Gas bubbling, odor Formation of a Solid precipitate forms

Chemical Equations A + B  C + D Left Side = Reactants (starting materials) Right Side = Products (ending materials) “” is read as “produces or yields” How show physical state of reactants & products? (s), (l), (g), (aq)

Law of Conservation of Matter Matter is neither created nor destroyed in a chemical reaction Mass reactants = Mass products Chemical bonds in reactants may break New bonds may form to produce products # atoms of each element MUST be same on both sides of equation

Coefficients in Chemical Equations Numbers in front of formulas are called coefficients apply to everything following in formula represent numbers of individual atoms, molecules or mole ratios (Remember the MOLE MAP!)

Writing Chemical Equations Begin with skeleton equation write correct chemical formulas of reactants and products Balance the skeleton equation Use the RAP table

Equation Balancing Create a RAP table table that shows type & # atoms present Example: Fe + O2 → Fe2O3 R A P Fe O 1 2 2 3

Balance Equation Use coefficients to make sure atoms are = Update RAP table as go along Double check your work Do one last pass to check that all # are same on both sides Coefficients must be in their lowest possible ratios Reduce if necessary

Example 1 Fe + O2 → Fe2O3 #R atoms #P 1 Fe 2 2 O 3 balance O’s by making 6 on each side Fe + 3 O2 → 2 Fe2O3 O’s are balanced - next balance Fe 4 Fe + 3 O2 → 2 Fe2O3 Make one last pass & count all atoms it’s balanced!!

Na + H2O → NaOH + H2 #R atoms #P 1 Na 1 2 H 3 1 O 1 make # H’s on right even Na + H2O → 2 NaOH + H2 balance Na’s by adding 2 2 Na + H2O → 2 NaOH + H2 One last pass: need to balance O and H on left 2 Na + 2 H2O → 2 NaOH + H2

2 AgNO3 + MgCl2  Mg(NO3)2 + AgCl Hint: can treat polyatomic [NO3-1] as one atom #R atom #P 1 Ag 1 1 NO3 2 1 Mg 1 2 Cl 1 Balance NO3-1 on the left with a 2 2 AgNO3 + MgCl2  Mg(NO3)2 + AgCl Balance Ag’s and Cl with a 2 2 AgNO3 + MgCl2  Mg(NO3)2 + 2 AgCl Make on last pass to count all atoms