The standard enthalpy of formation of substance in its standard state is zero.
Enthalpy is defined as a thermodynamic quantity that describes the energy of a system. For substances in their standard state, the enthalpy of formation is zero.
The standard state of a substance is defined as the state in which it is found under standard conditions. The following substances has their standard ethalpy of formation as zero or not zero;
Zero enthalpy of formation Non zero enthalpy of formation
Cl2(g) I2(s)
Br(g) Br2(l)
I2(g) Br2(s)
Hg(l) Hg(s)
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Moles are used conveniently in chemistry especially in stoichiometric calculations involving reactions. The unit of mole is a collective term that holds 6.022×10^23 particles. These particles is a general term for any small units of matter including molecules, atoms and sub-particles. This ratio of 6.022×10^23 particles to 1 mole is known to be the Avogadro's number. Its exact number is actually <span>6.0221409</span>×10^23. We use this constant in our stoichiometric calculation as follows:
15 moles oxygen * (6.022×10^23 molecules/ 1 mole oxygen) = 9.033×10^24 molecules of oxygen
The volume of 0.98 mol oxygen gas at 275 k and a pressure of 2.0 atm is 11.06L.
<h3>How to calculate volume?</h3>
The volume of a given mass of gas can be calculated using the following formula:
PV = nRT
Where;
- P = pressure
- V = volume
- R = gas law constant
- T = temperature
- n = number of moles
According to this question, 0.98 moles of oxygen gas at 275 k contains a pressure of 2.0 atm. The volume is calculated as follows:
2 × V = 0.98 × 0.0821 × 275
2V = 22.13
V = 11.06L
Therefore, the volume of 0.98 mol oxygen gas at 275 k and a pressure of 2.0 atm is 11.06L.
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