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REVERSIBLE REACTIONS

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 2NO 2 (g) N 2 O 4 (g). CHEMICAL EQUILIBRIUM.

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REVERSIBLE REACTIONS

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  1. 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)

  2. 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.

  3. LE CHATELIER’S 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.

  4. LE CHATELIER’S 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?

  5. LE CHATELIER’S 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)

  6. LE CHATELIER’S PRINCIPLE • Example:Consider 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?

  7. LE CHATELIER’S 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.

  8. LE CHATELIER’S 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?

  9. LE CHATELIER’S 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?

  10. LE CHATELIER’S 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?

  11. EQUILIBRIUM CONSTANT The ratio of product concentrations to reactant concentrations at equilibrium Shows: Whether the reactants (Keq<1) or products (Keq >1) are favored in a reaction aA + bB  cC + dD Keq = [C]c[D]d [A]a[B]b 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.

  12. 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

  13. pH < 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

  14. pH > 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

  15. DEFINITIONS OF ACIDS/BASES

  16. DEFINITIONS OF ACIDS/BASES

  17. ACIDS

  18. 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

  19. 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-

  20. Which number is larger? • 1.0 x 10-7 or 1.0 x 10-5 • 2.8 x 10-11 or 1.0 x 10-7 • 3.2 x 10-2 or 1.0 x 10-7 • 1.0 X 10-7 or 3.7 x 10-13

  21. 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

  22. Solutions If [H+] increases than [OH-] must decrease If [OH-] increases than [H+] must decrease

  23. 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

  24. 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?

  25. 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+)

  26. 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

  27. 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-]

  28. 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?

  29. pH: The negative logarithm of the hydrogen-ion concentration pH = -log[H+] • 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? • The pH of an unknown solution is 6.35. What is its hydrogen-ion concentration? • What is the pH of a solution if [OH-] = 4.0 x 10-11 M? • 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

  30. Indicator • Its acid and base forms have different colors

  31. 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

  32. 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 

  33. 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

  34. 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?

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