Textbook Question
How much work (in J) is involved in a chemical reaction if
the volume decreases from 33.6 L to 11.2 L against a constant
pressure of 90.5 kPa?
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Ch.5 - Thermochemistry
Chapter 5, Problem 35
Assume that 2 moles of water are formed according to the following reaction at constant pressure (101.3 kPa) and constant temperature (298 K): 2 H2(g) + O2(g) → 2 H2O(l). (b) Calculate _x001F_E for the reaction using your answer to (a).
Verified step by step guidance1
Step 1: Understand the reaction and the concept of enthalpy change (ΔE). The reaction given is 2 H2(g) + O2(g) → 2 H2O(l). The enthalpy change for a reaction at constant pressure is related to the heat absorbed or released.
Step 2: Use the standard enthalpy of formation values to calculate the enthalpy change for the reaction. 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.
Step 3: Write the expression for the enthalpy change of the reaction (ΔH_rxn) using the standard enthalpies of formation: ΔH_rxn = [2 * ΔH_f^°(H2O(l))] - [2 * ΔH_f^°(H2(g)) + ΔH_f^°(O2(g))].
Step 4: Recognize that the standard enthalpy of formation for elements in their standard state, such as H2(g) and O2(g), is zero. Therefore, the expression simplifies to ΔH_rxn = 2 * ΔH_f^°(H2O(l)).
Step 5: Use the known value of ΔH_f^°(H2O(l)) from a data table to calculate ΔH_rxn. This will give you the enthalpy change for the formation of 2 moles of water under the given conditions.
Related Practice
Open Question
(c) For a given process at constant pressure, _x001F_H is negative. Is the process endothermic or exothermic?
Open Question
(a) Under what condition will the enthalpy change of a process equal the amount of heat transferred into or out of the system? (b) During a constant-pressure process, the system releases heat to the surroundings. Does the enthalpy of the system increase or decrease during the process? (c) In a constant-pressure process, _x001F_H = 0. What can you conclude about _x001F_E, q, and w?
Open Question
Suppose that the gas-phase reaction 2 NO(g) + O2(g) → 2 NO2(g) were carried out in a constant-volume container at constant temperature. (a) Would the measured heat change represent _x001F_H or _x001F_E? (b) If there is a difference, which quantity is larger for this reaction? (c) Explain your answer to part (b).
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 methane, CH4(g), to form H2O(l) and CO2(g) at constant pressure releases 890 kJ of heat per mole of CH4. (a) Write a balanced thermochemical equation for this reaction.