Table of contents

1. Matter and Measurements4h 31m
2. Atoms and the Periodic Table5h 23m
3. Ionic Compounds2h 18m
4. Molecular Compounds2h 18m
5. Classification & Balancing of Chemical Reactions3h 17m
6. Chemical Reactions & Quantities2h 27m
7. Energy, Rate and Equilibrium3h 46m
8. Gases, Liquids and Solids3h 25m
9. Solutions4h 10m
10. Acids and Bases3h 29m
11. Nuclear Chemistry56m
BONUS: Lab Techniques and Procedures1h 38m
BONUS: Mathematical Operations and Functions47m
12. Introduction to Organic Chemistry1h 34m
13. Alkenes, Alkynes, and Aromatic Compounds2h 12m
14. Compounds with Oxygen or Sulfur1h 6m
15. Aldehydes and Ketones1h 1m
16. Carboxylic Acids and Their Derivatives1h 11m
17. Amines39m
18. Amino Acids and Proteins1h 51m
19. Enzymes1h 37m
20. Carbohydrates1h 41m
21. The Generation of Biochemical Energy2h 8m
22. Carbohydrate Metabolism2h 22m
23. Lipids2h 26m
24. Lipid Metabolism1h 45m
25. Protein and Amino Acid Metabolism1h 37m
26. Nucleic Acids and Protein Synthesis2h 54m

7. Energy, Rate and Equilibrium

Thermochemical Equations

GOB Chemistry

7. Energy, Rate and Equilibrium

Thermochemical Equations

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3:46 minutes

Problem 72b

Textbook Question

For the evaporation of water, H₂O(l) → H₂O(g), at 100°C, ∆H = +9.72 kcal/mol (+40.7 kJ/mol).
b. How many kilojoules are released when 10.0 g of H₂O(g) is condensed?

Verified step by step guidance

Step 1: Understand the problem. The condensation of water is the reverse of evaporation. Since evaporation absorbs energy (endothermic, ∆H = +40.7 kJ/mol), condensation releases the same amount of energy (exothermic, ∆H = -40.7 kJ/mol).

Step 2: Convert the mass of water (10.0 g) to moles. Use the molar mass of water (H₂O), which is approximately 18.02 g/mol. The formula to calculate moles is: moles = mass / molar mass.

Step 3: Calculate the energy released during condensation. Multiply the number of moles of water by the enthalpy change for condensation (∆H = -40.7 kJ/mol). The formula is: energy released = moles × ∆H.

Step 4: Ensure the correct sign for the energy change. Since condensation is exothermic, the energy released will be negative, indicating that energy is leaving the system.

Step 5: Double-check the units and ensure the final answer is in kilojoules (kJ). If necessary, confirm that all intermediate calculations are consistent with the given data.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Enthalpy of Vaporization

The enthalpy of vaporization is the amount of energy required to convert a unit mass of a substance from liquid to gas at a constant temperature and pressure. For water, this value is positive when vaporizing, indicating energy absorption. Conversely, during condensation, the same amount of energy is released, which is crucial for calculating energy changes in phase transitions.

Molar Mass of Water

The molar mass of water (H2O) is approximately 18.02 g/mol. This value is essential for converting between grams of water and moles, allowing for the calculation of energy changes based on the number of moles involved in the phase change. Understanding molar mass is fundamental in stoichiometry and thermodynamic calculations.

Energy Conversion

Energy conversion refers to the process of changing energy from one form to another. In this context, it involves converting the energy associated with the phase change of water from gas to liquid, quantified in kilojoules. Recognizing how to convert between different energy units (e.g., kcal to kJ) is vital for accurate calculations in thermodynamics.