Chemistry Mid Term Exam 2024-2025

The graph shows the variation of the first ionisation energy with proton number for some elements. The letters used are not the actual symbols for the elements. Which statement about the elements is correct?

• A P and X are in the same period in the Periodic Table.

• B The general increase from Q to X is due to increasing atomic radius.

• C The small decrease from R to S is due to decreased shielding.

• D The small decrease from U to V is due to repulsion between paired electrons.

Which row is correct? shape of H3O+ shape of SCl2

• A pyramidal and non-linear

• B pyramidal and linear

• C trigonal planar and non-linear

• D trigonal planar and linear

Which particle contains 8 protons, 9 neutrons and 10 electrons?

• A

• B

• C

• D

When an evacuated glass bulb of volume 200 cm 3 is filled with a gas at 300 K and 101 kPa, the mass of the bulb increases by 0.68 g. The gas obeys the ideal gas equation. What is the identity of the gas?

• A argon

• B krypton

• C neon

• D nitrogen

The standard enthalpy of formation of NO 2 (g) is +33.2 kJ mol–1 .

The standard enthalpy of formation of N 2 O 4 (g) is +9.2 kJ mol–1 . What is the standard enthalpy change for the reaction 2NO2 (g) → N2 O4 (g)?

• A –57.2 kJ mol –1

• B –24.0 kJ mol –1

• C +42.4 kJ mol –1

• D +75.6 kJ mol –1

A student reacts 1 mol of magnesium powder in a sealed 0.030 m3 container of oxygen at a pressure of 2.0 × 10 5 Pa and a temperature of 600 K. The magnesium reacts completely to form MgO. Which percentage of the oxygen will be used up?

• A 5.0%

• B 10%

• C 42%

• D 83%

Which equation represents an enthalpy change that is the average bond energy of the

C–H bond in methane?

When hydrogen iodide is reacted with concentrated sulfuric acid, several reactions occur, Which row gives the change in oxidation number of iodine and of sulfur in this reaction?

• A –1 and +6

• B –1 and +8

• C +1 and –6

• D +1 and –8

Some bond energies are listed. One mole of hydrogen reacts with oxygen to give water vapour. Using the bond energy data, what is the value for the enthalpy change of this reaction?

• A +221 kJ mol –1

• B +6 kJ mol –1

• C –242 kJ mol –1

• D –417 kJ mol –1

Hydrogen iodide is added to an evacuated reaction vessel. The vessel is sealed and warmed. A decomposition reaction occurs. Hydrogen and iodine are formed. Some hydrogen iodide remains. When equilibrium is established, the total pressure is 1.20 × 10 5 Pa. The partial pressure of hydrogen is 4.00 × 10 3 Pa. Hydrogen iodide, hydrogen and iodine are all gaseous under the conditions used. What is the value of K p for the equilibrium at this temperature, assuming the decomposition is the forward reaction?

• A 1.19 × 10 –3

• B 1.28 × 10 –3

• C 1.38 × 10 –3

• D 1.43 × 10 –3