Homework Help: Chemistry

Posted by John on Wednesday, July 21, 2010 at 5:58pm.

1.What is the molar heat of vaporization of water, given the following thermochemical equations?

H2 + 1/2 O2 --> H2O + 241.8 kJ

H2 + 1/2 O2 --> H2O + 285.5 kJ

a) 44.0 kJ/mol
b)-44.0 kJ/mol
c)241.8 kJ/mol

2. Which substance has a standard enthalpy of formation delta Hf, equal to zero?

a)Gold
b)water ( liquid state)
c)carbon monoxide
d)zinc
e)water (gas)

I can't seem to get the correct answer...

Chemistry - DrBob222, Wednesday, July 21, 2010 at 8:23pm
Isn't the answer to #1 just the difference between the liquid and the gas (which you didn't label)? And since we are talking vaporization, that must be +.

For #2, elements are defined as having Hf = zero; therefore, both Au and Zn qualify.

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