Q1. Balance the equation: Cu₂S(s) + O₂(g) → Cu₂O(s) + SO₂(g). Then identify the coefficient of SO₂ in the lowest whole-number equation.

Background

Topic: Chemical Equations & Stoichiometry

This question tests your ability to balance a chemical equation and identify the correct stoichiometric coefficient for a product.

Key Terms and Formulas:

• Balancing equations: Ensuring the same number of atoms of each element on both sides.

• Coefficient: The number in front of a chemical formula indicating the number of units.

Step-by-Step Guidance

1. Write out the unbalanced equation: .

2. Count the atoms of each element on both sides (Cu, S, O).

3. Adjust coefficients to balance Cu, S, and O atoms, starting with the element that appears least often.

4. Check that all atoms are balanced and that coefficients are the lowest whole numbers.

Try solving on your own before revealing the answer!

Q2. For the reaction N₂O₄(g) → 2 NO₂(g), ΔH° = +57.2 kJ per reaction as written. How much heat is absorbed when 18.4 g of NO₂(g) is produced?

Background

Topic: Thermochemistry – Enthalpy and Stoichiometry

This question tests your ability to relate the enthalpy change of a reaction to the amount of product formed using stoichiometry

.

Key Terms and Formulas:

• : Standard enthalpy change

• Molar mass of NO₂:

• Stoichiometry: Relating moles of product to enthalpy change

Step-by-Step Guidance

1. Calculate the moles of NO₂ produced: .

2. Determine how many "reactions" this corresponds to, given that 2 moles NO₂ are produced per reaction.

3. Set up a proportion to find the heat absorbed for the calculated number of reactions.

4. Multiply the number of reactions by to find the total heat absorbed.

Try solving on your own before revealing the answer!

Q3. Which types of nuclear radiation carry electric charge, and what is the sign of each charge?

Background

Topic: Nuclear Chemistry – Types of Radiation

This question tests your knowledge of the properties of alpha, beta, and gamma radiation, specifically their electric charge.

Key Terms:

• Alpha particles (): Helium nuclei

• Beta particles (): Electrons or positrons

• Gamma rays (): Electromagnetic radiation

Step-by-Step Guidance

1. Recall the composition of each type of radiation.

2. Identify which types are particles and which are electromagnetic waves.

3. Determine the charge of alpha and beta particles (positive, negative, or neutral).

4. State the sign of the charge for each charged particle.

Try solving on your own before revealing the answer!

Q4. Explain the trend in first ionization energy among elements in Groups 1, 2, 17, and 18.

Background

Topic: Periodic Trends – Ionization Energy

This question tests your understanding of how first ionization energy varies across different groups in the periodic table.

Key Terms:

• First ionization energy: Energy required to remove the first electron from an atom.

• Groups: Columns in the periodic table (1 = alkali metals, 2 = alkaline earth metals, 17 = halogens, 18 = noble gases).

Step-by-Step Guidance

1. Recall the general trend for ionization energy across a period and down a group.

2. Compare the typical values for Groups 1, 2, 17, and 18.

3. Explain why Group 1 elements have low ionization energies and Group 18 have high values.

4. Discuss the effect of electron configuration and nuclear charge on these trends.

Try solving on your own before revealing the answer!

Q5. Write the mathematical relationship described by Boyle’s law and state the conditions under which it applies.

Background

Topic: Gas Laws – Boyle’s Law

This question tests your knowledge of Boyle’s law and the conditions required for its validity.

Key Formula:

Where:

• = pressure

• = volume

Step-by-Step Guidance

1. State Boyle’s law in mathematical form.

2. Identify the variables that must remain constant (temperature and amount of gas).

3. Explain that Boyle’s law describes the inverse relationship between pressure and volume.

4. Describe the conditions (constant temperature and fixed amount of gas) under which the law applies.

Try solving on your own before revealing the answer!