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Questions Regarding Equilibrium Reactions

1. Given the following reaction

H2(g) + I2 (s) = 2HI (g) ¤h = + 68.0 KJ/mol

A) Write the Kc expression.

B) State whether the number of moles of H2 (g) in the container will increase, decrease, or remain the same after each of the following disturbances is applied to the original mixture. For each case, assume that all other variables remain constant except for the given disturbance

I) HI is removed
Ii) Iodine is pulverised
Iii) The temperature of the reaction vessel is increased
Iv) Volume of the reaction vessel is doubled
V) The pressure is increased by adding neon gas
Vi) A catalyst is added

C) For each of the above instances where the shift leads to a change in Kc , state whether it will increase or decrease

2. For each of the following identify the strongest. ( Explain )

A) Acid. C2H5COOH or C2H5OH

B) Acid : Zn2+ or Pb2+
One which is above in the reactivity series is stronger
C) Base : F- or CN-

D) Acid : HBrO2 or HBrO3

E) Acid : HIO or HCIO

F) Base : HPO4 2- or H2PO4-

4. The graph below shows the result of the titration of a 25ml sample of a 0.10 M solution of a weak acid , HA with a strong base , 0.10M NaOH

(see attached file for graph)

A) describe two features of the graph above that identify HA as a weak acid

B) describe one method by which the value of the acid- dissociation constant for HA can be determined using the graph above
Graph attached separately
C) on the graph above , sketch the titration curve that would result if 25ml of 0.10M HCL were used instead of 0.10M HA

D) from the data below , select the most appropriate indicator for the titration. Justify your answer

Indicator. pKa
Methyl Red. 5.5
Bromothymol Blue. 7.1
Phenolphthalein. 8.7

5. In a saturated solution of MgF2 at 18C , the concentration of Mg2+ is 1.21 x 10-3 molar. The equilibrium is represented by the equation below

MgF2(s) = Mg2+ (aq) + 2F- (aq)

A) Write the expression for the solubility -product , Ksp , and calculate its value at 18C

B) Predict whether a precipitate of MgF2 will form when 100.0 mls of 3.00 x 10-3 molar Mg(NO3)2 solution is mixed with 200.0 mls of a 2.00 x 10-3 molar NaF solution at 18C.

Calculations to support your prediction must be shown

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1. Given the following reaction

H2(g) + I2 (s) = 2HI (g) ¤h = + 68.0 KJ/mol
A) write the Kc expression

KC = products / reactants
= [HI]2 / [H2]
Note: I2 is a reactant, but because it is a solid it is considered equal to 1.

B) state whether the number of moles of H2 (g) in the container will increase , decrease or remain the same after each of the following disturbances is applied to the original mixture. For each case , assume that all other variables remain constant except for the given disturbance

I) HI is removed
-Product is removed so reaction will shift right: decrease in H2.
Ii) Iodine is pulverized
-More surface area for H2 to react with: decrease in H2.
Iii) the temperature of the reaction vessel is increased
-Reaction is endothermic because heat is positive. Increase in temp shifts reaction to the right because temp can be treated like a reactant. Decrease in H2.
Iv) Volume of the reaction vessel is doubled
-When the volume increases the reaction will shift towards side with greater number of gas molecules. There are 2 gas molecules on the right, so reaction shifts towards the right. Decrease in H2.
V) The pressure is increased by adding neon gas
-When the pressure increases the reaction will shift towards side with fewer number of gas molecules. There is 1 gas molecule on the left, so ...

Solution Summary

This solution provides answers to various questions regarding equilibrium questions.

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