已知:(1)C(s)+O2(g)=CO2(g),△rHmθ(298.15)=-393.5kJ/mol (2)H2(g)+1/2O2(g)=H2O(1),△rHmθ(298.15)=-285.8kJ/mol (3)CH4(g)+2O2(g)=CO2(g)+2

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问题 已知:(1)C(s)+O2(g)=CO2(g),△rHmθ(298.15)=-393.5kJ/mol
(2)H2(g)+1/2O2(g)=H2O(1),△rHmθ(298.15)=-285.8kJ/mol
(3)CH4(g)+2O2(g)=CO2(g)+2H2O(1),△rHmθ(298.15)=-890.4kJ/mol,则甲烷的标准摩尔生成△rHmθ(298.15,CH4,g)为(    )kJ/mol。

选项 A、74.7
B、-74.7
C、211.1
D、-211.1

答案B

解析 甲烷的标准摩尔生成反应为:
    C(s)+2H2(g)=CH4(g),△rHmθ(298.15,CO2,g)
    由于(4)=(1)+2(2)-(3)
    故△rHmθ(298.15,CO2,g)=(-393.5)+2×(-285.8)-(-890.4)=-74.7 kJ/mol,
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