Which of the following substances have a standard heat of formation of zero?
O2 at 25.O degrees C and 1 atm
Fe at 1200 degrees C
C2H6 at standard conditions
Cl2 at 2 atm
O2, Fe and Cl2 should all have zero enthalpy of formation because, they are pure or in diatomic state. However, Fe and Cl2 are not under standard conditions because standard condition is 25degreesC at 1atm. So to me it should be O2.
O2 is right.
To determine which of the given substances have a standard heat of formation of zero, we need to consider the definition of standard heat of formation.
The standard heat of formation is the enthalpy change when one mole of a substance is formed from its elements in their standard states, under standard conditions (usually 25°C and 1 atm). If the substance is an element in its standard state, its standard heat of formation is typically taken as zero.
Let's analyze each substance to determine if their standard heat of formation is zero:
1. O2 at 25.0 degrees C and 1 atm: Oxygen gas (O2) is an element in its standard state. Therefore, its standard heat of formation is zero.
2. Fe at 1200 degrees C: Iron (Fe) is not in its standard state. Therefore, its standard heat of formation is not zero.
3. C2H6 at standard conditions: Ethane (C2H6) is a compound, not an element. Therefore, its standard heat of formation is usually not zero.
4. Cl2 at 2 atm: Chlorine gas (Cl2) is also an element in its standard state. Therefore, its standard heat of formation is zero.
In summary, the substances with a standard heat of formation of zero are O2 at 25.O degrees C and 1 atm and Cl2 at 2 atm.
To determine which of the given substances have a standard heat of formation of zero, we need to know the standard heat of formation values for each substance. The standard heat of formation refers to the heat released or absorbed when one mole of a compound is formed from its elements in their standard states at a given temperature and pressure.
Here's how you can find the information:
1. Look up the standard heat of formation value for each substance in a reliable reference source. One commonly used source is a thermodynamic database, such as the NIST Chemistry WebBook or a reputable chemistry textbook.
2. Search for the standard heat of formation values for O2, Fe, C2H6, and Cl2. Note that the values might be specific to different temperatures and pressures, so make sure to find the appropriate values for the conditions specified in the question.
3. Compare the obtained values to zero. If the standard heat of formation value for a substance is zero, it means that no heat is released or absorbed during the formation of one mole of that substance from its elements in their standard states.
Based on the information you provided, we don't have the necessary data to determine which of the substances have a standard heat of formation of zero. You would need to find the specific standard heat of formation values for each substance at the specified conditions (temperature and pressure) to make the comparison.