general chemistry 100

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  1. What is the pH of a solution prepared by dissolving 2.50 g of NaOH(s) in 2.500 L of H2O(l)?
  2. (a) When 0.100 mol of HNO3 dissolves in 500.0 mL H2O(l), what ions are produced and what are their concentrations?
    (b) When 0.200 mol of NaOH dissolves in 500.0 mL H2O(l), what ions are produced and what are their concentrations?

    (c) Suppose the solutions described in parts (a) and (b) are mixed. At the moment of mixing, before any chemical reaction takes place, what ions are present and what would their concentrations be? (Be careful to note the total volume after mixing!)

    (d) Write a balanced chemical equation for the reaction between hydronium and hydroxide ions.

    (e) When this reaction takes place in the solution described in part (c), what is the limiting reagent — that is, which reagent will be consumed first?

    (f) What is the excess reagent and what concentration of this species remains after reaction?

    (g) What is the pH of the resulting solution?

  3. What is the pH of a solution resulting from mixing solutions of HClO3 (0.200 M, 125.0 mL) and KOH (0.200 M, 75.0 mL)? (15 points)
  4. Nitrous acid (HNO2) is a weak acid with a pKa of 3.29.(a) What is the value of Ka for nitrous acid?(b) Write the formula for the conjugate base of nitrous acid (this species is called nitrite ion).(c) What are the values of Kb and pKb for nitrite ion?
  5. Ethylamine (CH3CH2NH2) is a weak base similar to ammonia, with a pKb value of 3.4.

(a) What is the value of Kb for ethylamine.

(b) Write the formula for the conjugate acid of ethylamine (this specis is called ethylammonium ion).

(c) What are the values of Ka and pKa for ethylammonium ion?

  1. Suppose that solutions containing equivalent chemical quantities of nitrous acid and ethylamine are mixed. Which side of the following equilibrium will be favored, and how do you know?
    HNO2(aq) + CH3CH2NH2(aq) ⇌ CH3CH2NH3+(aq) + NO2–(aq)
  2. The reaction shown below does not take place spontaneously under standard conditions at room temperature, but occurs readily at temperatures above 1000 K. (15 points)
    C(s) + CO2(g) ⟶ 2 CO(g)
    (a) What is the sign of ∆G° at 25°C, and how do you know?

    (b) What is the sign of ∆G° above 1000°C, and how do you know?

    (c) What is the sign of ∆S°, and how do you know?

    (d) What is the sign of ∆H°, and how do you know?

    (e) What is the sign of ∆Ssurr when this reaction takes place spontaneously, and how do you know?

    (f) What is the sign of ∆Suniv when this reaction takes place spontaneously, and how do you know?

  3. The combustion of ethylene (C2H4) is both spontaneous (∆G° = –1314.1 kJ/mol) and highly exothermic (∆H° = –1323.0 kJ/mol) in the standard state at 25°C.

    (a) Use the data in the problem statement to determine the value of ∆S° for the combustion of ethylene at 25°C.
    (b) Above what temperature will this reaction become non-spontaneous (that is, at what temperature will ∆G° = 0)? (Hint: The correct answer here is almost absurdly large, so don’t let that freak you out.)

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