XPD009 Foundation Chemistry

Foundation Studies Program

XPD009 / Foundation Chemistry

Qu 1.Oceans cover 71% of the surface of the Earth and act as a carbon sink, absorbing about 25% of carbon dioxide produced by humans. Since the industrial revolution, the concentration of carbon dioxide in the atmosphere has increased and as this dissolves into the oceans, the pH of the oceans becomes more acidic.

Once dissolved in water at saturation point, the carbon dioxide reacts with water to form carbonic acid. The carbonic acid rapidly ionises to form hydrogen carbonate ions and hydronium ions (H3O+). Sea water is also saturated with aqueous carbonate ions.

Write the equations and include the relevant states of each species for:

The formation of carbonic acid [2]

The formation of hydronium ions when carbonic acid reacts with water. [1]

Qu 2.Nitrogen dioxide is toxic to humans when inhaled and is a significant component of air pollution. It can be formed by the combustion of nitrogen in the air at high temperatures; firstly forming nitric oxide NO(g) and on further oxidation, forming nitrogen dioxide, NO2(g). The equation for the process is given:

The following questions relate to the equilibrium system represented by this equation. (8 marks)

Write the equilibrium expression for this reaction when it is in equilibrium. [2]

{" "} [NO2]2

Kc= ______________

[N2] [O2] 2

Assuming all other conditions remain constant, what happens to the equilibrium constant after the pressure of the system is lowered and equilibrium is re-established. [1]

If we change pressure of the system, Equilibrium constant does not change. Equilibrium Constant does not depends on pressure changes.

On the axes below, draw the forward (-----) and reverse (- - -) reaction rates, starting at the moment the oxygen and nitrogen gases begin to react with each other until after the equilibrium has been established at time A. Continue the graph until time B. [3]


On the same axes above, draw and label clearly the effect of conducting the same reaction at a higher temperature. [2]

Ans: At higher temperature, the rate of reaction increases.

Qu 3. Ammonia exists in equilibrium with hydrogen and nitrogen as shown by the following exothermic equation. (6 marks)

As they exist in the gaseous state, the relative concentrations can be given in terms of the partial pressure (kPa) of each gas.

Nitrogen, hydrogen, and ammonia gases are placed in a rigid container and allowed to reach equilibrium. The graph below shows the partial pressures of the gaseous system initially at equilibrium. After the experiment operates for 4 minutes, a change is imposed upon it.

What characteristic of equilibrium is indicated on the graph by the section from 0 to 4 minutes? [1]

From 0 to 4 minutes the system is in equilibrium.

A change was imposed on the graph at 4 minutes. What imposed change could have produced the results indicated on the graph? [1]

At 4 minutes the Extra volume of H2 added. As a result the formation of product (NH3) increased and N2 is consumed.

The system was suddenly cooled at 8 minutes and then reached equilibrium at 12 minutes. Using this information, complete the graph above from 8-12 minutes. [4]

Ans: Since it is a exothermic reaction. When temperature decreases the equilibrium shift to right side.

So the availability of NH3 will increases in the system at 8 minutes. Similarly the N2, H 2 will participate in the reaction and the availability decreases. After some time (12 minutes) all are comes to the equilibrium. The graph is as shown below.