REVERSIBLE REACTIONS

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REVERSIBLE REACTIONS

• A reaction in which the conversion of reactants
  to products and the conversion of products to
  reactants occur simultaneously
• is the symbol which represents a reversible
  reaction
• 2NO2(g) N2O4(g)

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CHEMICAL EQUILIBRIUM

• Chemical equilibrium happens in a reversible
  reaction, when the rate at which a substance
  reacts is exactly the same as the rate at which
  it is being produced.
• 2NO2(g) N2O4(g)
• In equilibrium the concentrations of NO2 N2O4
  would not change.

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LE CHATELIERS PRINCIPLE

• When a change happens to a reaction at
  equilibrium, the reaction will shift to reduce
  the effects of that change.
• Concentration
• If more of a substance is added, the
  concentration of that substance increases. More
  of that substance will be used and the reaction
  will shift towards the other side of the
  equation.
• If substance is removed, the concentration of
  that substance decreases, and the reaction will
  shift to create more of that substance.

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LE CHATELIERS PRINCIPLE

• Consider the following chemical reaction at
• equilibrium
• H2CO3(aq) ? CO2(aq) H2O(l)
• What will adding more CO2 do to the equilibrium?
• What will adding more H2CO3 do to the
  equilibrium?

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LE CHATELIERS PRINCIPLE

• When a change happens to a reaction at
  equilibrium, the reaction will shift to reduce
  the effects of that change.
• Temperature (kJ in an equation)
• If temperature is added to a system the reaction
  will shift away from the side of the reaction
  that requires heat.
• If the temperature of a system decreases, the
  reaction will shift towards the side of the
  reaction that requires heat.
• 50 kJ NH4Cl(s) NH3(g) HCl(g)

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LE CHATELIERS PRINCIPLE

• ExampleConsider the following chemical reaction
  at equilibrium
• 2SO2(g) O2(g) ? 2SO3(g) 22 kJ
• What effect will heating this reaction have on
  its equilibrium?
• b) What effect will cooling this reaction have
  on its equilibrium?

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LE CHATELIERS PRINCIPLE

• When a change happens to a reaction at
  equilibrium, the reaction will shift to reduce
  the effects of that change.
• Pressure (comes from the moles of gas)
• If the total pressure of a system is increased,
  the system will shift to reduce that pressure by
  proceeding in the direction that produces fewer
  molecules of gas.

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LE CHATELIERS PRINCIPLE
Consider the following chemical reaction at
equilibrium 2SO2(g) O2(g) ? 2SO3(g)
heat What effect will adding pressure to this
reaction have on its equilibrium? What effect
will decreasing the pressure of this reaction
have on its equilibrium?
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LE CHATELIERS PRINCIPLE
Consider the following chemical reaction at
equilibrium 2SO2(g) O2(g) ? 2SO3(g)
heat What effect will adding pressure to this
reaction have on its equilibrium? What effect
will decreasing the pressure of this reaction
have on its equilibrium?
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LE CHATELIERS PRINCIPLE
Consider the following reaction at
equilibrium PCl5(g) heat ? PCl3(g)
Cl2(g) What could be done to this system to
increase the amount of PCl3 produced? What
could be done to this system to increase the
amount of PCl5 produced?
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EQUILIBRIUM CONSTANT

• The ratio of product concentrations to reactant
• concentrations at equilibrium
• Shows Whether the reactants (Keqlt1) or
  products (Keq gt1) are favored in a reaction
• aA bB ? cC dD
• Keq Cc?Dd
• Aa?Bb

The reversible reaction N2(g) 3H2(g) ?
2NH3(g) produces ammonia, which is a fertilizer.
At equilibrium, a 1 L flask contains 0.15 mol
H2, 0.25 mol N2, and 0.10 mol NH3. Calculate the
Keq for the reaction.
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Solubility Product Constant

• Same as the equilibrium constants but only shows
  the ion concentrations (as that is what is
  dissolved in the solution)
• Shows how soluble the compound is
• The lower the solubility product constant, the
  lower the solubility of the compound

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• pH lt 7
• Sour/tart taste
• Electrolytes in solution
• React with many metals to produce hydrogen gas
• React with bases to form water and salt
• Will change the color of an indicator
• Acidic solutions can be formed when nonmetal
  oxides react with water

ACIDS
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• pH gt 7
• Bitter taste
• Slippery feel
• Electrolytes as aqueous solutions
• Will cause an indicator to change color
• React with acids to form water and salt
• Basic solutions can be formed when a metal oxide
  reacts with water

Bases
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DEFINITIONS OF ACIDS/BASES
ACID BASE
Arrhenius Hydrogen-containing compounds that ionize to yield hydrogen ions (H) in aqueous solution Compounds that ionize to yield hydroxide ions (OH-) in aqueous solution
Bronsted-Lowry Hydrogen-ion donor Hydrogen-ion acceptor
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DEFINITIONS OF ACIDS/BASES
ACID BASE
Arrhenius Start with H (hydrogen ion) Hydrogen-containing compounds that ionize to yield hydrogen ions (H) in aqueous solution End with OH (hydroxide ion) Compounds that ionize to yield hydroxide ions (OH-) in aqueous solution
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ACIDS
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CONJUGATE ACID/BASE PAIRS

• Consists of two substances related by the loss or
  gain of a single hydrogen ion (H)
• Conjugate acid Particle formed when a base
  gains a hydrogen ion (H)
• Hydronium Ion (H3O) A water molecule that
  gains a hydrogen ion and becomes positively
  charged
• Conjugate base The particle that remains when
  an acid has donated a hydrogen ion

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Acid (donates H) Conjugate Base
HCl
HNO3
Base (accept H) Conjugate Acid
OH-
NH3
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CONJUGATE ACID/BASE PAIRS

• Identify the acid, base, conjugate acid and
• conjugate base in each equation.
• HCl NH3 ? NH4 Cl-
• HCO3- HCl ? H2CO3 Cl-
• HCO3-1 OH- ? H2O CO32-

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ACID (donates a H) BASE (Accepts H) Conjugate Acid (Accepted H) Conjugate Base

HClNH3 ? NH4 Cl- HClNH3 ? NH4 Cl- HClNH3 ? NH4 Cl- HClNH3 ? NH4 Cl-
NH4 H2O

HPO4-2 NO3-

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Which number is larger?

1. 1.0 x 10-7 or 1.0 x 10-5
2. 2.8 x 10-11 or 1.0 x 10-7
3. 3.2 x 10-2 or 1.0 x 10-7
4. 1.0 X 10-7 or 3.7 x 10-13

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Neutral Solutions
OH- H if the solution is neutral
pH of H2O 7
If H is greater than OH- than the solution
is acidic If OH- is greater than H than the
solution is basic
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Solutions
If H increases than OH- must decrease If
OH- increases than H must decrease
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Mathematical formula to link the concentration of
H to OH- 1 x 10-14 H x OH- If the
solution is neutral than H OH- H
1.0 x 10-7 OH- 1.0 x 10-7 If the solution
is acidic than H is larger than 1.0 x 10-7 If
the solution is basic than OH- is larger than
1.0 x 10-7
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1 x 10-14 H x OH-

• If the H in a solution is 1.0 x 10-5 M, what
  is the OH- of this solution? Is this solution
  acidic, basic or neutral?

• 2) If the hydroxide ion concentration of an
  aqueous solution is 1 x 10-3 M, what is the H
  in the solution? Is this solution acidic, basic
  or neutral?

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Self-Ionization of Water

• Happens when the collisions between water
  molecules are
• energetic enough to transfer a hydrogen ion from
  one water
• molecule to another.
• Hydrogen ions in solution are called
• Protons Hydrogen Ions (H) Hydronium Ions
  (H3O)

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Neutral Solutions

• Water is neutral so a neutral solution would have
  equal concentrations of H and OH-
• In pure water at equilibrium, the product of the
  hydrogen-ion concentration and the hydroxide ion
  concentration equals 1.0 x 10-14
• H x OH- 1.0 x 10-14
• So in a neutral solution
• H 1.0 x 10-7
• OH- 1.0 x 10-7

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• In equilibrium, if H increases the OH- will
  decrease (more H2O must be produced to balance
  equilibrium)
• If H decreases the OH- will increase (more
  H2O will react to balance the equilibrium)
• 1 x 10-14 H x OH-

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• Acidic Solution One in which the H is
  greater than the OH-
• The H concentration is greater than 1 x 10-7
• Basic (Alkaline) Solution One in H is less
  than OH-
• The OH- concentration is greater than 1 x 10-7

• If the H in a solution is 1.0 x 10-5 M, is the
  solution acidic, basic or neutral?
• a) What is the OH- of this solution?

• 2) If the hydroxide ion concentration of an
  aqueous solution is 1 x 10-3 M, what is the H
  in the solution?
• a) Is this solution acidic, basic or neutral?

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pH The negative logarithm of the hydrogen-ion
concentration

• pH -logH

• A neutral solution has a H 1.0 x 10-7. What
  is the pH of the neutral solution?
• a) What is the pH of an acidic solution?
• b) What is the pH of a basic solution?

• Find the pH of each of the following solutions
• H 1 x 10-4 M
• H 0.0015 M
• H 1.0 x 10-12 M

1. The pH of an unknown solution is 6.35. What is
   its hydrogen-ion concentration?
2. What is the pH of a solution if OH- 4.0 x
   10-11 M?

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Indicator

• Its acid and base forms have different colors

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NEUTRALIZATION REACTIONS

• The reaction between an acid and a base
• An acid and a base react in an aqueous solution
  to produce a salt and water (which are both
  neutral)
• Salt Compound consisting of an anion from an
  acid and a cation from a base

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NEUTRALIZATION REACTIONS

• Write complete balanced equations for the
• following acid-base reactions.
• a) H2SO4(aq) KOH(aq) ?
• b) H3PO4(aq) Ca(OH)2(aq) ?
• c) HNO3(aq) Mg(OH)2 ?

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TITRATION

• Adding a known amount of solution of known
  concentration to determine the concentration of
  another solution
• Standard Solution The solution of known
  concentration
• End Point The point at which the indicator
  changes color
• Happens At The point of neutralization

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TITRATION

• How to Calculate the Concentration from a
  Titration
• MaVa MbVb M Molarity
• V Volume
• Example A 25 mL solution of H2SO4 is completely
  neutralized by 18
• mL of 1.0 M NaOH. What is the concentration of
  the H2SO4 solution?