Final Examination
IPS*1200
Principles of Modern Chemistry

April 14, 1999

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1. A 1.61 g sample of asparagus is placed into a calorimeter at 22.79 C under an excess pressure of oxygen. A spark ignites the combustion process, the asparagus is completely oxidized, and the temperature of the calorimeter rises to 23.69 C. The calorimeter constant was previously measured to be 5.39 kJ/K. What is the enthalpy change for this process per gram of asparagus?

The temperature rise in the calorimeter is .

The enthalpy change that gave rise to this temperature rise must be (given the calorimeter constant as 5.39 kJ/K) .

The enthalpy per gram of asparagus is just .

2. Calculate the enthalpy of formation of HCl (g), namely, the reaction . Use the following experimental data:

We need adjust the equations and scale them, so that their sum equals the equation we need.

3. The reaction to produce methanal (formaldehyde) from hydrogen and carbon monoxide occurs with a standard enthalpy of reaction of +1.96 kJ and a standard entropy of reaction of -109.58 J/K.

Calculate the entropy change in the surroundings (per mole of methanal produced) and comment on the spontaneity of the reaction at 25 C.

The enthalpy change in the surroundings arises from the heat transferred to or from it by the system. In this case, the system has a positive enthalpy of reaction, so heat flows into it from the surroundings. We have

The universe entropy change is the sum of this with the entropy change in the system.

A negative entropy change in the universe indicates a non-spontaneous process.

4. The complete hydrogenation of acetylene (ethyne) to ethane is written as

Given the enthalpy and entropy of formation for acetylene and ethane as follows:

Determine the Gibbs Free Energy of reaction at 600 K, assuming that the enthalpy and entropy are constant with respect to temperature changes.

Determine the enthalpy and entropy changes, assume they are constant with temperature, and solve for the change in the Gibbs function.

5. Determine the equilibrium constant for the reaction

at 100 C. The given data is for 25 C.

Same thing except carry this on to calculate the equilibrium constant.

6. Balance the following redox reaction in acidic media:

Balance the equation a follows:

7. What is the standard cell potential for the following galvanic cell?

Very easy: Cathode minus anode and anode is written first in cell definition.

8. Determine the concentration of Pb2+ in the cell if the potential measured is 0.40 V.

The standard reduction half-potentials are also given.

We first need to know DE. The cell, as written, has identified the lead as the anode, so lead is being oxidized.

With the Nernst equation, we can determine the lead concentration present.

9. Provide an appropriate IUPAC name for each of the following organic compounds:

(a)

3-bromo-4-phenylhexanal

(b)

methyl 4-methylhexanoate

(c)

1-bromo-2-iodocyclopentane

10. (a) Which substance is more soluble in water, butanol or hexanol?

Butanol is more soluble in water

(b) In order to impress your date, what would you put on for a fragrance, an amine or an ester?

Better wear an ester; amine as pretty ugly smelling.

(c) Which would have a higher boiling point, propane or propanoic acid?

Propanoic acid will have a higher boiling point. Those oxygens will tend to provide some hydrogen bonding to keep things in the liquid phase longer.

(d) Which of the following are secondary alcohols; 3,3-dimethylbutanol; 1,1-butanediol; 2-methyl-2-propanol; 3,4-dibromo-2-pentanol.

The first is a primary alcohol; the second is a primary diol; the third is a tertiary alcohol; only fourth, 3,4-dibromo-2-pentanol is a secondary alcohol.

Last update:23 April 1999
Comments to: Dan Thomas