Exam 2 Study Guide: Chemistry Concepts and Problem-Solving

Q1. The image in Figure 1 is best described as:

Background

Topic: Atomic Spectra

This question tests your understanding of atomic emission and absorption spectra, specifically for hydrogen.

Key Terms:

• Emission spectrum: Light emitted by atoms when electrons drop to lower energy levels.

• Absorption spectrum: Light absorbed by atoms when electrons move to higher energy levels.

• Hydrogen spectrum: Characteristic lines produced by hydrogen atoms.

Step-by-Step Guidance

1. Examine Figure 1 and note the pattern of lines shown.

2. Recall the difference between emission and absorption spectra: emission spectra show bright lines on a dark background, while absorption spectra show dark lines on a bright background.

3. Consider whether the lines in Figure 1 are bright or dark, and what that indicates about the type of spectrum.

Try solving on your own before revealing the answer!

Final Answer: The emission spectrum of hydrogen

Figure 1 shows bright lines on a dark background, which is characteristic of an emission spectrum.

Q2. Group trends and order on the Periodic Table

Background

Topic: Periodic Table Trends

This question tests your knowledge of how atomic radius, ionization energy, and electronegativity change across periods and groups.

Key Terms:

• Atomic radius: Size of an atom.

• Ionization energy: Energy required to remove an electron.

• Electronegativity: Ability of an atom to attract electrons.

Step-by-Step Guidance

1. Recall that atomic radius increases down a group and decreases across a period.

2. Ionization energy and electronegativity generally increase across a period and decrease down a group.

3. Use the periodic table to compare elements in the same group or period.

Try solving on your own before revealing the answer!

Final Answer: Atomic radius increases down a group, decreases across a period; ionization energy and electronegativity increase across a period, decrease down a group.

These trends are due to changes in electron shielding and nuclear charge.

Q3. The products in the complete combustion of octane (C8H18) are:

Background

Topic: Combustion Reactions

This question tests your ability to identify the products of a hydrocarbon combustion reaction.

Key Terms:

• Complete combustion: Reaction with oxygen producing carbon dioxide and water.

• Hydrocarbon: Compound made of hydrogen and carbon.

Step-by-Step Guidance

1. Write the general equation for complete combustion of a hydrocarbon: $\text{C}_x\text{H}_y + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O}$

2. Identify the products: carbon dioxide and water.

3. Balance the equation if needed, but focus on the products for this question.

Try solving on your own before revealing the answer!

Final Answer: Carbon dioxide (CO2) and water (H2O)

Complete combustion always produces CO2 and H2O as products.

Q4. The specific heat of water is 4.18 J/g·K and iron is 0.45 J/g·K. If equal masses of water and iron are heated, which substance will experience the greater temperature change?

Background

Topic: Specific Heat and Temperature Change

This question tests your understanding of how specific heat affects temperature change when equal masses are heated.

Key Terms and Formula:

• Specific heat ($c$): Amount of heat required to raise the temperature of 1 gram of a substance by 1 K.

• Formula: $q = mc\Delta T$

Step-by-Step Guidance

1. Recall that $q$ is the heat added, $m$ is mass, $c$ is specific heat, and $\Delta T$ is temperature change.

2. For equal masses and equal heat added, the substance with lower specific heat will have a greater $\Delta T$.

3. Compare the specific heat values for water and iron.

Try solving on your own before revealing the answer!

Final Answer: Iron will experience the greater temperature change.

Because iron has a lower specific heat, it heats up more for the same amount of energy.

Q5. A balloon with initial volume of 1.0 L at 300 K and 1.0 atm is heated to 340 K and expanded to a final pressure of 1.5 atm. What is the final volume?

Background

Topic: Combined Gas Law

This question tests your ability to use the combined gas law to solve for the final volume of a gas when temperature and pressure change.

Key Formula:

• Combined Gas Law: $\frac{P_1V_1}{T_1} = \frac{P_2V_2}{T_2}$

• $P_1$, $V_1$, $T_1$ = initial pressure, volume, temperature

• $P_2$, $V_2$, $T_2$ = final pressure, volume, temperature

Step-by-Step Guidance

1. Identify the known values: $P_1 = 1.0$ atm, $V_1 = 1.0$ L, $T_1 = 300$ K, $P_2 = 1.5$ atm, $T_2 = 340$ K.

2. Plug these values into the combined gas law formula.

3. Rearrange the formula to solve for $V_2$: $V_2 = \frac{P_1V_1T_2}{P_2T_1}$

4. Check that all units are consistent (atm, L, K).

Try solving on your own before revealing the answer!

Final Answer: $V_2 \approx 0.67$ L

Using the combined gas law and plugging in the values, you find the final volume is less than the initial volume due to increased pressure.