Ch.9 - Thermochemistry: Chemical Energy

McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook

McMurry 8th Edition

Ch.9 - Thermochemistry: Chemical Energy

Problem 6b

Chapter 9, Problem 6b

Several processes are given in the table and labeled as endo- thermic or exothermic and given a sign for ∆H°. Which process is labeled with the correct sign of ∆H° and correct classification as endothermic or exothermic? (LO 9.8) Process (b) Methane, the main component of natural gas, is burned to produce a flame on a stovetop.

Verified step by step guidance

Identify the type of process: Burning methane is a combustion reaction.

Recall that combustion reactions are typically exothermic, meaning they release heat.

Understand that for exothermic reactions, the change in enthalpy (\( \Delta H^\circ \)) is negative because energy is released to the surroundings.

Consider the context: Methane combustion produces heat and light, consistent with an exothermic process.

Conclude that the correct classification for the process of burning methane is exothermic with a negative \( \Delta H^\circ \).

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Key Concepts

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

Endothermic and Exothermic Reactions

Endothermic reactions absorb heat from their surroundings, resulting in a positive change in enthalpy (∆H° > 0). In contrast, exothermic reactions release heat, leading to a negative change in enthalpy (∆H° < 0). Understanding these classifications is crucial for determining the energy changes associated with chemical processes.

Enthalpy Change (∆H°)

Enthalpy change (∆H°) is a measure of the heat content of a system at constant pressure. It indicates whether a reaction is endothermic or exothermic based on the heat absorbed or released during the process. A negative ∆H° signifies an exothermic reaction, while a positive ∆H° indicates an endothermic reaction.

Combustion of Methane

The combustion of methane (CH₄) is an exothermic reaction where methane reacts with oxygen (O₂) to produce carbon dioxide (CO₂) and water (H₂O), releasing energy in the form of heat and light. This process is commonly used in heating and cooking, exemplifying an exothermic reaction with a negative ∆H°.

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Combustion Apparatus

Related Practice

Textbook Question

Several processes are given in the table and labeled as endo- thermic or exothermic and given a sign for ∆H°. Which process is labeled with the correct sign of ∆H° and correct classification as endothermic or exothermic? (LO 9.8) Process (c) Water freezes into ice in the freezer.

For which of the following reactions are ΔE and ΔH equal? (a) CO2(g) + H2O(l) → H2CO (b) 2 NaHCO3 (s) → Na2CO3(s) + H2O(g) + CO2(g) (c) 2 H2(g) + O2(g) → 2 H2O(g) (d) CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g)

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Textbook Question

How much heat is required to raise a 50.0 g piece of iron from 25 °C to its melting point of 1538 °C? The specific heat capacity for iron is 0.451 J/g•°C. (a) 34.1 kJ (b) 168 kJ (c) 12.1 kJ (d) 6.78 kJ

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Textbook Question

A room-temperature balloon filled with air is placed in the freezer and the balloon contracts. What is the sign of q and w for the air inside the balloon? (LO 9.4) (a) q = +, w = - (b) q = +, w = + (c) q = -, w = - (d) q = -, w = +

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Textbook Question

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