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Chemistry: Equilibrium Concentration Sample Questions

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a) What is the expression for the eqilibrium constant K in terms of the concentrations of the products and reactants for the reaction between ammonia, (NH3 (aq)) (SMALL 3), WHICH REACTS WITH WATER TO PRODUCE AMMONIUM (NH4 + (aq))
and hydroxide (OH - (aq)) ions.

NH3 (aq) + H20 (l) = NH4+ (aq) + OH- (aq)

the enthalpy change is +3.5kj mol

Using the equilbrium expression (from above) calculate What the OH- (aq) ion concentration in an ammonia solution with an equilibrium concentration of
1.00 x 10-2 mol dm-3 (ie 10 to the power -2)
the concentration of water at 25 degrees celcius is 55.4 mol dm-3
and the value of the equilibrium constant K for the reaction is 3.19 x 10-7
(ie 10 to the power -7). the answer needs to be to 3 significant figures.

b) use the calculated value for OH- (aq) ion concentration together with the expression for the ion product of water to calculate the H+ (aq) ion concentration. Calculate the PH for the ammonia solution
Assume that Kw = 1.00 x 10-14 mol2 dm-6 (ie 10 to the power -14)
at 25 degrees celcius, the answer needs to be to 3 significant figures.

Thanks! I just don't seem to get this!

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finding equilibrium constant, OH- concentration ................
1A)
What is the expression for the eqilibrium constant K in terms of the concentrations of the products and reactants for the reaction between ammonia, (NH3 (aq)) (SMALL 3), WHICH REACTS WITH WATER TO PRODUCE AMMONIUM (NH4 + (aq))
and hydroxide (OH - (aq)) ions.

NH3 (aq) + H20 (l) = NH4+ (aq) + OH- (aq)

the enthalpy change is +3.5kj mol

using the equilbrium expression (from above) ...

Solution Summary

This solution provides assistance with the problem regarding equilibrium concentration.

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General Chemistry

Kc for the reaction below at 25°C is 4.8 x 10-6. Calculate the
equilibrium concentration (mol/L) of Cl2(g) if the initial
concentration of ICl(g) is 1.33 mol/L. There is no I2 or Cl2
initially present.

2ICl(g) <-> I2(g) + Cl2(g)

a. 6.4 x 10-6
b. 343
c. 3.2 x 10-6
d. 2.9 x 10-3
e. 5.8 x 10-3

2. Consider the following reaction at equilibrium:
2NH3(g) <-> N2(g) + 3H2(g) &#916;H° = +92.4 kJ

Adding N2(g) to the system at equilibrium will __________.

a. decrease the concentration of H2(g) at equilibrium
b. remove all of the H2(g)
c. cause the reaction to shift to the right
d. increase the value of the equilibrium constant
e. decrease the concentration of NH3(g) at equilibrium

3. Consider the following reaction at equilibrium:

2CO2(g) <-> 2CO(g) + O2(g) (Traingle sign)H° = 514 kJ
Increasing the temperature will ________.

a. decrease the concentration of CO2(g)
b. shift the reaction to the right
c. increase the concentration of CO
d. increase the concentration of O2(g)
e. decrease the value of the equilibrium constant

3. The effect of a catalyst on a chemical reaction is to
_______________.

a. accelerate the forward reaction only
b. lower the energy of the transition state
c. make reactions more exothermic
d. increase the entropy change associated with a reaction
e. react with product, effectively removing it and shifting the
equilibrium to the right

4. Consider the equilibrium at 25°C:
1A(g) + 2B(g) <-> 3C(g) + D(L) Kc = 3.25 x 10-2
What is the value of Kp?

a. 19.453700
b. 80.521090
c. 0.136915
d. 0.000156
e. 0.032500

5. Consider the equilibrium at 25°C:
2A(g) + 2B(g)<-> 1C(g) + D(L) Kp = 2.65 x 10-4
What is the value of Kc?

a. 4030182.628
b. 3.881
c. 1586.224730
d. 0.002291
e. 2379.556

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