Which of the following substances have a standard heat of formation (ÄHf°) of zero?
O2(g) at 25.0 degree C and 1 atm
Fe at 1200 degree C
C2H6(g) at standard conitions
Cl2(g) at 2 atm
O2 @ 25 C and 1 atm is the only one.
Fe yes but at 25 C, not 1200.
C2H6 no since it's a compound.
Cl2 yes at 25 C and 1 atm but not at 2 atm.
The right answer is O2
when an sample of air with a volume of 1.5 L at 1.25 atm and 25 degree celcius is cooled to -4 degree celcius the pressure reduces to 0.80 atm what is the new volume of the sample?
Well, well, well, let's see which of these substances has a standard heat of formation of zero!
Hmm, let me think. Okay, first up we have O2(g) at 25.0 degrees C and 1 atm. Well, oxygen is quite a high-maintenance element, and it definitely doesn't have a heat of formation of zero. So scratch that one off the list.
Moving on, we have Fe at 1200 degrees C. Now, iron might be getting pretty hot there, but it still doesn't have a standard heat of formation of zero. Sorry, iron, you're out.
Next up, we have C2H6(g) at standard conditions. Ah, good old ethane. Now, I hate to break it to you, but ethane also has a nonzero standard heat of formation. So close, but no cigar.
Lastly, we have Cl2(g) at 2 atm. Chlorine, chlorine, chlorine... you never cease to amaze me. And by that, I mean you also have a nonzero standard heat of formation.
So, the verdict is... none of the above substances have a standard heat of formation of zero. Tough luck! Better luck next time, my friend.
To determine which of the substances have a standard heat of formation (ΔHf°) of zero, we need to look up the standard heat of formation values for each substance.
The standard heat of formation (ΔHf°) is the change in enthalpy that occurs when one mole of a substance is formed from its elements in their standard states, usually at 25°C and 1 atm.
Let's check the standard heat of formation values for each substance:
1. O2(g) at 25.0°C and 1 atm: The standard heat of formation of O2(g) is zero because O2 is the naturally occurring form of oxygen in its standard state.
2. Fe at 1200°C: Since Fe is not a compound, it doesn't have a standard heat of formation value. Only compounds have defined standard heat of formation values.
3. C2H6(g) at standard conditions: To determine the standard heat of formation of C2H6(g), we need to look up the value. The standard heat of formation of C2H6(g) is -84.68 kcal/mol. Therefore, C2H6(g) does not have a standard heat of formation of zero.
4. Cl2(g) at 2 atm: To determine the standard heat of formation of Cl2(g), we need to look up the value. The standard heat of formation of Cl2(g) is 0 kcal/mol. Therefore, Cl2(g) has a standard heat of formation of zero.
So, out of the given substances, only O2(g) and Cl2(g) have a standard heat of formation value of zero.