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Ch.5 - Thermochemistry
All textbooksBrown 15th EditionCh.5 - ThermochemistryProblem 40b
Chapter 5, Problem 40b

The decomposition of Ca(OH)2 into CaO(s) and H2O at constant pressure requires the addition of 109 kJ of heat per mole of Ca(OH)2 . b. Draw an enthalpy diagram for the reaction.

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Draw a horizontal line to represent the enthalpy level of the reactants, Ca(OH)_2.
Since the reaction is endothermic, draw an upward arrow from the reactants' line to indicate the absorption of heat.
Label the upward arrow with the amount of heat absorbed, 109 kJ/mol.
Draw another horizontal line above the reactants' line to represent the enthalpy level of the products, CaO and H_2O.
Label the products' line with the chemical formulas of the products, CaO(s) and H_2O(g).

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Key Concepts

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

Enthalpy (ΔH)

Enthalpy is a thermodynamic property that represents the total heat content of a system at constant pressure. It is defined as the sum of the internal energy and the product of pressure and volume. In chemical reactions, the change in enthalpy (ΔH) indicates whether a reaction is exothermic (releases heat) or endothermic (absorbs heat), which is crucial for understanding the energy changes during the decomposition of Ca(OH)₂.
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Decomposition Reaction

A decomposition reaction is a type of chemical reaction where a single compound breaks down into two or more simpler products. In this case, calcium hydroxide (Ca(OH)₂) decomposes into calcium oxide (CaO) and water (H₂O). Understanding the nature of decomposition reactions helps in predicting the products and the energy changes involved, such as the heat required for the reaction to proceed.
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Enthalpy Diagram

An enthalpy diagram, or reaction coordinate diagram, visually represents the energy changes during a chemical reaction. It typically shows the enthalpy of the reactants and products, along with the activation energy and the overall change in enthalpy (ΔH). For the decomposition of Ca(OH)₂, the diagram would illustrate the energy input required (109 kJ) to break the bonds in the reactant, leading to the formation of products at a higher energy level.
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Related Practice
Textbook Question

A gas is confined to a cylinder under constant atmospheric pressure, as illustrated in Figure 5.4. When 0.49 kJ of heat is added to the gas, it expands and does 214 J of work on the surroundings. What are the values of H and E for this process?

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Textbook Question

The complete combustion of ethanol, C2H5OH(l), to form H2O(g) and CO2(g) at constant pressure releases 1235 kJ of heat per mole of C2H5OH. b. Draw an enthalpy diagram for the reaction.

Textbook Question

Ozone, O3(g), is a form of elemental oxygen that plays an important role in the absorption of ultraviolet radiation in the stratosphere. It decomposes to O2(g) at room temperature and pressure according to the following reaction: 2 O3(g) → 3 O2(g) ΔH= -284.6 kJ b. Which has the higher enthalpy under these conditions, 2 O3(g) or 3 O2(g)?

Textbook Question

Without referring to tables, predict which of the following has the higher enthalpy in each case: (a) 1 mol CO2(s) or 1 mol CO2(g) at the same temperature

Textbook Question

Without referring to tables, predict which of the following has the higher enthalpy in each case: (b) 2 mol of hydrogen atoms or 1 mol of H2