Which of the following substances shown should the standard heat of formation (\DeltaΔHfo be zero at 25oC
GaPO4 (aq)
As (l)
Ar (s)
Br2 (l)
dHo formation Br2(l) = 0
Well, let's see. We're looking for a substance with a standard heat of formation (\(\Delta H_{f}^{o}\)) of zero at 25°C.
Oh, I've got it! The substance that fits the bill is Ar(s), which stands for Argon in its solid state. In other words, it's ice-cold to the point where even its heat of formation is zero. That's some seriously chill chemistry!
To determine which of the given substances should have a standard heat of formation (\(\Delta H_f^o\)) of zero at 25°C, we need to refer to the definition of standard heat of formation.
The standard heat of formation (\(\Delta H_f^o\)) of a substance is the enthalpy change when one mole of the compound is formed from its elements in their standard states at a given temperature and pressure. In other words, it represents the heat released or absorbed during the formation of one mole of the compound.
Based on this definition, a substance will have a \(\Delta H_f^o\) of zero if it is found in its most stable form at that particular temperature. When a substance is in its most stable form, no additional heat is needed for its formation, resulting in a \(\Delta H_f^o\) value of zero.
Now let's analyze each of the given substances:
1. GaPO4 (aq): This is an aqueous solution of gallium phosphate. Since it's in the form of an aqueous solution, it is not its most stable form. Therefore, GaPO4 (aq) will not have a \(\Delta H_f^o\) of zero at 25°C.
2. As (l): This represents liquid arsenic. Liquid arsenic is already in its most stable form at 25°C. Therefore, As (l) will have a \(\Delta H_f^o\) of zero at 25°C.
3. Ar (s): This represents solid argon. Argon is an inert noble gas and exists as a monatomic solid at 25°C, which is its most stable form. Therefore, Ar (s) will have a \(\Delta H_f^o\) of zero at 25°C.
4. Br2 (l): This represents liquid bromine. Bromine is a diatomic element and exists as a liquid at 25°C, which is its most stable form. Therefore, Br2 (l) will have a \(\Delta H_f^o\) of zero at 25°C.
Based on the analysis, the substances that should have a \(\Delta H_f^o\) of zero at 25°C are As (l), Ar (s), and Br2 (l).
To determine which substance has a standard heat of formation (\(ΔH_{fo}\)) of zero at 25°C, we need to consider the definition of standard heat of formation.
The standard heat of formation is the enthalpy change that occurs when one mole of a compound is formed from its constituent elements in their standard states at a given temperature and pressure. The standard state of an element is typically its most stable form at a specific temperature and pressure, which is often 25°C and 1 atmosphere.
In this case, we have four substances: GaPO4 (aq), As (l), Ar (s), and Br2 (l). Let's examine each one:
1. GaPO4 (aq): This substance is an aqueous solution of GaPO4. Aqueous solutions are not considered standard states for most compounds because the concentration of the solution can vary. Therefore, GaPO4 (aq) does not have a standard heat of formation of zero.
2. As (l): Liquid arsenic (As) is not the standard state of arsenic. The standard state of arsenic is a solid (gray crystalline form). Therefore, As (l) does not have a standard heat of formation of zero.
3. Ar (s): Argon (Ar) is a noble gas, and its standard state is the gas phase. Therefore, solid argon (Ar (s)) is not at its standard state and does not have a standard heat of formation of zero.
4. Br2 (l): Bromine (Br2) normally exists as a liquid at room temperature and pressure. Since liquid bromine is at its standard state, it has a standard heat of formation of zero at 25°C.
Therefore, among the given substances, Br2 (l) is the one that should have a standard heat of formation (\(ΔH_{fo}\)) of zero at 25°C.