Q5.1 When vinegar (CH3COOH) and baking soda (NaHCO3) are combined, the mixture spontaneously undergoes an endothermic reaction while releasing CO2 gas. Would the test tube feel hot or cold? Do you think this reaction would have a + or – value for ΔG? Explain your reasoning.

Background

Topic: Thermodynamics and spontaneity of chemical reactions

This question tests your understanding of endothermic reactions, spontaneity, and the concept of Gibbs free energy (ΔG).

Key Terms and Formulas:

• Endothermic reaction: A reaction that absorbs heat from its surroundings.

• ΔG (Gibbs free energy): Determines whether a reaction is spontaneous. Formula:

• Spontaneous reaction: Occurs without external input; ΔG is negative.

Step-by-Step Guidance

1. Recall that an endothermic reaction absorbs heat, so the surroundings (test tube) lose heat.

2. Think about how the test tube would feel if heat is absorbed from it (would it feel hot or cold?).

3. Consider the spontaneity: The reaction occurs spontaneously, so what does that tell you about the sign of ΔG?

4. Use the formula to relate enthalpy (ΔH), entropy (ΔS), and temperature (T) to spontaneity.

5. Set up your reasoning for why the sign of ΔG is what it is, based on the reaction being endothermic and spontaneous.

Try solving on your own before revealing the answer!

Q5.2 In your own words, define free energy change, ΔG.

Background

Topic: Gibbs Free Energy

This question is about understanding the concept of free energy change and its role in determining reaction spontaneity.

Key Terms and Formulas:

• ΔG (Gibbs free energy): The energy available to do work in a chemical reaction.

• Exergonic reaction: ΔG is negative; energy is released.

• Endergonic reaction: ΔG is positive; energy is absorbed.

Step-by-Step Guidance

1. Write a brief definition of ΔG in your own words, focusing on its meaning in chemistry.

2. For part (a), compare exergonic and endergonic reactions in terms of ΔG.

3. For part (b), recall which sign of ΔG indicates a spontaneous reaction.

4. Think about examples of spontaneous and non-spontaneous reactions to reinforce your answer.

Try solving on your own before revealing the answer!

Q5.3 Classify the following as exothermic or endothermic reactions:

• a. When two solids are combined in a test tube, the test tube gets hot.

• b. A reaction must be heated for it to continue.

Background

Topic: Thermochemistry

This question tests your ability to distinguish between exothermic and endothermic reactions based on heat flow.

Key Terms and Formulas:

• Exothermic: Releases heat to surroundings.

• Endothermic: Absorbs heat from surroundings.

Step-by-Step Guidance

1. For part (a), consider what it means if the test tube gets hot after combining solids.

2. For part (b), think about why a reaction would need to be heated to continue.

3. Recall the definitions of exothermic and endothermic reactions and match them to each scenario.

Try solving on your own before revealing the answer!

Q5.4 Classify the following as exergonic or endergonic reactions:

• a. On a reaction energy diagram, the reactants show lower energy than the products.

• b. On a reaction energy diagram, the products are lower in energy than the reactants.

Background

Topic: Reaction energetics

This question tests your understanding of energy changes in chemical reactions and how to interpret energy diagrams.

Key Terms and Formulas:

• Exergonic: Energy is released; products have lower energy than reactants.

• Endergonic: Energy is absorbed; products have higher energy than reactants.

Step-by-Step Guidance

1. For part (a), compare the energy levels of reactants and products and decide if energy is absorbed or released.

2. For part (b), do the same comparison and classification.

3. Use the definitions of exergonic and endergonic to classify each scenario.

Try solving on your own before revealing the answer!

Q5.7 Would the sign of ΔS be + or – for the following changes?

• a. Water freezing to form ice

• b. A protein being formed from amino acids

• c. Digestion of a meal

Background

Topic: Entropy (ΔS)

This question tests your ability to predict the sign of entropy change for different processes.

Key Terms and Formulas:

• ΔS (entropy change): Measures disorder or randomness.

• Positive ΔS: Increase in disorder.

• Negative ΔS: Decrease in disorder.

Step-by-Step Guidance

1. For each scenario, consider whether the process increases or decreases molecular disorder.

2. Recall that freezing water forms a more ordered solid, protein formation organizes amino acids, and digestion breaks down complex molecules.

3. Assign the sign of ΔS based on your reasoning for each process.

Try solving on your own before revealing the answer!

Q5.8 Would the sign of ΔS be + or – for the following changes?

• a. Liquid gasoline burning to form carbon dioxide and steam

• b. Cleaning up your bedroom

• c. A stick of dynamite exploding

Background

Topic: Entropy (ΔS)

This question tests your ability to predict entropy changes in various scenarios.

Key Terms and Formulas:

• ΔS (entropy change): Measures disorder or randomness.

Step-by-Step Guidance

1. For each scenario, decide if the process increases or decreases disorder.

2. Burning gasoline produces gases, cleaning up increases order, and an explosion increases disorder.

3. Assign the sign of ΔS for each process.

Try solving on your own before revealing the answer!

Q5.9 Classify the following as spontaneous or nonspontaneous processes:

• a. A hot bowl of oatmeal cooling on the table

• b. A chemical reaction that gives off free energy

Background

Topic: Spontaneity of processes

This question tests your understanding of spontaneous and nonspontaneous processes in thermodynamics.

Key Terms and Formulas:

• Spontaneous process: Occurs naturally without external input.

• Nonspontaneous process: Requires external energy.

Step-by-Step Guidance

1. For part (a), think about whether oatmeal cooling happens naturally.

2. For part (b), recall that reactions releasing free energy are typically spontaneous.

3. Classify each process based on your reasoning.

Try solving on your own before revealing the answer!

Q5.10 Classify the following as spontaneous or nonspontaneous processes:

• a. Walking on a treadmill at the gym

• b. A chemical reaction that requires free energy

Background

Topic: Spontaneity of processes

This question tests your understanding of what makes a process spontaneous or nonspontaneous.

Key Terms and Formulas:

• Spontaneous process: Occurs without external input.

• Nonspontaneous process: Requires external energy.

Step-by-Step Guidance

1. For part (a), consider whether walking on a treadmill happens without energy input.

2. For part (b), recall that reactions requiring free energy are not spontaneous.

3. Classify each process based on your reasoning.

Try solving on your own before revealing the answer!