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

Endothermic & Exothermic Reactions

GOB Chemistry

7. Energy, Rate and Equilibrium

Endothermic & Exothermic Reactions

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0:51 minutes

Problem 25a

Textbook Question

The vaporization of Br₂ from the liquid to the gas state requires 7.4 kcal/mol (31.0 kJ/mol).
a. What is the sign of ∆H for this process? Write a reaction showing heat as a product or reactant.

Verified step by step guidance

Understand the concept of enthalpy change (∆H): Enthalpy change is the heat absorbed or released during a chemical or physical process at constant pressure. For endothermic processes, ∆H is positive, and for exothermic processes, ∆H is negative.

Identify the type of process: Vaporization is the process of converting a liquid into a gas. This requires energy input to overcome intermolecular forces, making it an endothermic process. Therefore, the sign of ∆H is positive.

Write the reaction for the vaporization of bromine (Br₂): The reaction can be written as Br₂(l) → Br₂(g).

Include heat in the reaction: Since the process is endothermic, heat is absorbed. Heat is written as a reactant in the reaction: Br₂(l) + heat → Br₂(g).

Summarize: The sign of ∆H for the vaporization of Br₂ is positive, and the reaction showing heat as a reactant is Br₂(l) + heat → Br₂(g).

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Key Concepts

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

Enthalpy Change (∆H)

Enthalpy change (∆H) is a measure of the heat content of a system during a process at constant pressure. A positive ∆H indicates that heat is absorbed from the surroundings, while a negative ∆H signifies that heat is released. In the context of vaporization, the process requires energy input, resulting in a positive ∆H.

Endothermic Process

An endothermic process is one that absorbs heat from its surroundings. In the case of vaporization, the transition of a substance from liquid to gas requires energy to overcome intermolecular forces. This absorption of heat is reflected in the positive value of ∆H, indicating that heat is a reactant in the reaction.

Chemical Reaction Representation

Chemical reactions can be represented with a balanced equation that includes reactants, products, and energy changes. For the vaporization of bromine (Br2), the reaction can be written as: Br2(l) + heat → Br2(g). This notation emphasizes that heat is required for the transition from liquid to gas, highlighting the endothermic nature of the process.

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Si(s) + 2Cl₂(g) → SiCl₄(g) + 157 kcal

b. Is the energy of the product higher or lower than the energy of the reactants?

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The equation for the formation of silicon tetrachloride from silicon and chlorine is Si(s) + 2Cl₂(g) → SiCl₄(g) + 657 kJ

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Oxygen can be converted into ozone by the action of lightning or electric sparks:

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Hydrogen chloride can be made from the reaction of chlorine and hydrogen:

Cl₂(g) + H₂(g) → 2 HCl(g)

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a. Is the reaction endothermic or exothermic?

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What is measured by the heat of reaction?

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The vaporization of Br2 from the liquid to the gas state requires 7.4 kcal/mol (31.0 kJ/mol). a. What is the sign of ∆H for this process? Write a reaction showing heat as a product or reactant.

Key Concepts

Enthalpy Change (∆H)

Endothermic Process

Chemical Reaction Representation

Watch next

The vaporization of Br₂ from the liquid to the gas state requires 7.4 kcal/mol (31.0 kJ/mol).
a. What is the sign of ∆H for this process? Write a reaction showing heat as a product or reactant.