Given the energy diagram above, what is ΔH when 0.5 mol of methane is combusted, forming H2O(g)?

Question

BlackTom AI · Accepted Answer

Restating the problem and options to set the stage:
Question: Given the energy diagram above, what is ΔH when 0.5 mol of methane is combusted, forming H2O(g)? Options: –404.5 kJ, +1618. kJ, –809.0 kJ, –1618 kJ, +404.5 kJ, +809.0 kJ.

Step-by-step analysis of each option:
Option 1: –404.5 kJ
This value represents half of the standard combustion enthalpy of CH4, assuming ΔHrxn for the full reaction (1.0 mol CH4 combusted) is about –809.0 kJ. Since the problem specifies 0.5 mol of CH4, the enthalpy change scales linearly with the amount of fuel. Therefore, ΔH = (0.5 mol / 1.0 mol) × (–809.0 kJ) = –404.5 kJ. This is consistent with the given ΔHrxn per mole and the amount used.

Option 2: +1618. kJ
Positive sign would imply an endothermic process, which contradicts the provided energy diagram where combustion of methane releases energy. Therefore this is incorrect.

Option 3: –809.0 kJ
This would be the enthalpy change for combusting 1.0 mol CH4 under the stated conditions. Since only 0.5 mol is reacting, using the full amount would overstate ΔH by a factor of two. Thus, this is not correct for 0.5 mol.

Option 4: –1618 kJ
This corresponds to combusting 2.0 mol CH4 (twice the standard 1.0 mol energy) or a doubled amount. With only 0.5 mol reacting, this would be four times too large in magnitude, so it is incorrect for the given quantity.

Option 5: +404.5 kJ
A positive value would indicate an endothermic process, which does not align with methane combustion being exothermic as shown in the diagram. This is incorrect.

Option 6: +809.0 kJ
Again, this implies endothermic behavior and is not consistent with the exothermic combustion of methane depicted. This is incorrect.

Summary rationale: The key idea is that the enthalpy change scales with the amount of reactant. The diagram provides ΔHrxn ≈ –809.0 kJ per 1.0 mol CH4 combusted. For 0.5 mol CH4, you divide by 2, yielding ΔH = –404.5 kJ. All other options either imply wrong sign, incorrect magnitude for the given amount, or misinterpret the stoichiometry.

Given the energy diagram above, what is ΔH when 0.5 mol of methane is combusted, forming H2O(g)?单项选择题

类似问题

The heat of combustion of ethane, C2H6, is 1560 kJ/mol. What is the heat of combustion of ethane, in kJ per gram?

Consider the equilibrium dissociation of N2O4(g) to NO2(g). N2O4(g) ⇌ 2NO2(g) Using your knowledge of Lewis structures and bond energies (bond breaking vs. bond forming) to predict whether this reaction is

Calculate H for the reaction of sulfur dioxide with oxygen. 2SO(g) + O(g) 2SO(g) (HSO(g) = –296.8 kJ/mol; HSO(g) = –395.7 kJ/mol)

Calculate the energy required to produce 7.00 mol ClO on the basis of the following balanced equation. 2Cl(g) + 7O(g) + 130 kcal 2ClO(g)

The amount of heat released by the complete burning of 1 mole of a substance is its ____.

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单