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Honors Chemistry Chapter 9

Honors Chemistry Chapter 9. Chemical Equations. 9.1 Representing Chemical Changes. Chemical Reaction – the process by which 1 or more substs are changes into 1 or more diff substs Correct equation shows: What changes take place

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Honors Chemistry Chapter 9

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  1. Honors Chemistry Chapter 9 Chemical Equations

  2. 9.1 Representing Chemical Changes • Chemical Reaction – the process by which 1 or more substs are changes into 1 or more diff substs • Correct equation shows: • What changes take place • Relative amts of various elems & comps that take part in these changes

  3. 9.1 Representing Chemical Changes • Reactants – starting substsina chemical rxn • Products – substs formed by the chemical rxn • 2C2H2(g) + 5O2(g) 4CO2(g) + 2H2O(l) • Reactants yield products • Letters in ( ) indicate physical state of easubst involved • (g) – gas, (l) – liquid, (s) or (cr) – solid (crystalline), (aq) – aqueous or water soln

  4. 9.2 Balancing Equations • To write a correct chemical eqn: • Determine reactants & products • Write reactants on left side connected w/ a + an write products on right side • Connect 2 sides w/ an arrow showing direction of rxn • SYMBOLS & FORMULAS MUST BE WRITTEN CORRECTLY 3. Balance eqn - show an = # of atoms of eaelem on both sides of the eqn

  5. 9.2 Balancing Equations 3. Balance eqn • show an = #of atoms of eaelem on both sides of the eqn • In a chemrxn, mass is not lost or gained • Same amt of matter before & after rxn • Same # & kind of atoms must be present on both sides of an eqn

  6. 9.2 Balancing Equations • Example: • C3H8 + O2 CO2 + H2O • C3H8 + 5 O23CO2+ 4H2O • Balance by changing only coefficients, never subscripts!

  7. 9.3 Classifying Chemical Changes • 6 General Types of Rxns • Single Displacement Rxn • 1 elem displaces another in a compound • Ex) Cl2 + 2KBr 2KCl + Br2 • Ex) 2Al + Fe2O3 Al2O3 + 2Fe • General Form: • elem + comp elem + comp • A + BX B + AX • X + AY Y + AX

  8. 9.3 Classifying Chemical Changes • Double Displacement Rxn(Ionic Rxn) • The (+) and (-) ions of 2 comps are interchanged • Ex) PbCl2 + Li2SO4 2LiCl + PbSO4 • Ex) ZnBr2 + 2AgNO3 Zn(NO3)2 + 2AgBr: • General Form: • Comp + comp comp + comp Or • AX + BY AY + BX

  9. 9.3 Classifying Chemical Changes • Neutralization • A special type of double displrxn • Acid + Base Salt (ionic comp) + water • Strong acid start w/ H, bases end in OH • Ex) HBr + NaOHNaBr + HOH • Ex) Ba(OH)2 + 2HNO3 Ba(NO3)2 + 2HOH

  10. 9.3 Classifying Chemical Changes • Decomposition • Subst breaks up into simpler substs when energy is supplied • Ex) CdCO3 CdO + CO2 • Ex) Pb(OH)2 PbO + H2O • General Form: • Comp 2 or more elems or comps • AB A + B • Energy may be heat, light, electricity, or mechanical shock

  11. 9.3 Classifying Chemical Changes • Synthesis • 2 or more substs combine to form 1 new subst (sometimes called composition rxn) • Ex) NH3 + HCl NH4Cl • Ex) 2H2 + O2 2H2O • General Form: • Elem or comp. + elem or comp comp • A + B AB

  12. 9.3 Classifying Chemical Changes • Combustion (of hydrocarbons) • Not usually considered one of the major types of rxns • Most organic comps will burn in air • Many are very flammable • When a comp burns in air, it is really reacting w/ oxygen in air • Combustion rxns are referred to as oxidation rxns • Products of the combustion of a hydrocarbon under normal conditions are CO2(g) & H2O(g)

  13. 9.3 Classifying Chemical Changes • Combustion (cont) • Ex) Methane (CH4) burns in air • CH4 + 2O2 CO2 + 2H2O • Ex) Butane (C4H10) burns in air • 2C4H10 + 13O2 8CO2 + 10H2O • General Form: • Hydrocarbon + oxygen CO2 + H2O

  14. 9.4 Mass-Mass Relationships • Balanced eqns represent the relationship betw the # of particles that react & the # of particles produced • There is also a relationship betw reacting masses & masses of products • The coefficients of a balanced eqn give the relative amts in moles of reactants & products.

  15. Mass-Mass Relationships • To solve mass-mass problems: • 1. Write a balancedeqn • Show rxn that is taking place • 2. Start w/ what your given & change to moles of given subst • 3. Using ratio of moles in the eqn, go to mole of required subst (what your asked for) • 4. Change from moles of required subst to grams • Work out prob (checking units)

  16. 9.5 Energy & Chemical Change • Chemical changes are always accompanied by a change in energy • Endothermic – a rxn in which energy is absorbed • Products are higher in energy than reactants • DHr = + • Exothermic – a rxn in which energy is released • Products are lower in energy than reactants • DHr = -

  17. 9.5 Energy & Chemical Change • All rxns require a certain minimum amtof energy to get started • - Activation Energy

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