Skip to main content
Ch.5 - Thermochemistry
Brown - Chemistry: The Central Science 15th Edition
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoBrown 15th EditionCh.5 - ThermochemistryProblema 70
Capitolo 5, Problema 70

What is the value of the standard enthalpy of formation of an element in its most stable form?

Guida verificata passo dopo passo
1
Identify the concept of standard enthalpy of formation, which is the change in enthalpy when one mole of a substance is formed from its elements in their standard states.
Recognize that the standard state of an element is its most stable form at 1 atm pressure and a specified temperature, usually 25°C (298 K).
Understand that for any element in its most stable form, the standard enthalpy of formation is defined as zero.
This definition is based on the convention that no energy is required to form an element from itself.
Therefore, the value of the standard enthalpy of formation for an element in its most stable form is always zero.

Risposta video verificata per un problema simile:

Questa soluzione video è stata consigliata dai nostri tutor come utile per risolvere questo problema.
Durata del video:
1m

Concetti chiave

Ecco i concetti essenziali che devi comprendere per rispondere correttamente alla domanda.

Standard Enthalpy of Formation

The standard enthalpy of formation (ΔH°f) is the change in enthalpy when one mole of a compound is formed from its elements in their standard states. It is a crucial concept in thermodynamics and helps in calculating the energy changes during chemical reactions.
Video consigliato:
Percorso guidato
02:34
Enthalpy of Formation

Most Stable Form of an Element

The most stable form of an element refers to its physical state and allotrope under standard conditions (1 atm pressure and 25°C). For example, the most stable form of carbon is graphite, while oxygen exists as O2 gas. This stability is essential for determining the standard enthalpy of formation.
Video consigliato:
Percorso guidato
02:35
Elemental Forms of Elements

Zero Enthalpy of Formation for Elements

The standard enthalpy of formation for any element in its most stable form is defined as zero. This serves as a reference point for calculating the enthalpy changes of compounds formed from these elements, simplifying thermodynamic calculations in chemistry.
Video consigliato:
Percorso guidato
02:34
Enthalpy of Formation
Pratica correlata
Domanda del libro di testo

Given the data N2(g) + O2(g) → 2 NO(g) ΔH = +180.7 kJ 2 NO(g) + O2(g) → 2 NO2(g) ΔH = -113.1 kJ 2 N2O(g) → 2 N2(g) + O2(g) ΔH = -163.2 kJ use Hess's law to calculate ΔH for the reaction N2O(g) + NO2(g) → 3 NO(g)

894
views
Domanda del libro di testo

Write balanced equations that describe the formation of the following compounds from elements in their standard states, and then look up the standard enthalpy of formation for each substance in Appendix C: (a) NH4NO3(s)

1
views
Domanda del libro di testo

For each of the following compounds, write a balanced thermochemical equation depicting the formation of one mole of the compound from its elements in their standard states and then look up H °f for each substance in Appendix C. (b) FeCl3(s)

2
views
Domanda del libro di testo

(c) What is meant by the term standard enthalpy of formation?

456
views
Domanda del libro di testo

We can use Hess's law to calculate enthalpy changes that cannot be measured. One such reaction is the conversion of methane to ethane: 2 CH4(g) → C2H6(g) + H2(g) Calculate the ΔH° for this reaction using the following thermochemical data: CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l) ΔH° = -890.3 kJ 2 H2(g) + O2(g) → 2 H2O(l) H° = -571.6 kJ 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(l) ΔH° = -3120.8 kJ

1171
views