Elements in Their Standard States

Oct 13, 2025 by miodeya.com 1 views

**Which Substances Have $$\Delta H_{f} = 0 \, \text{kJ/mol}$$ by Definition?**

Introduction In chemistry, the standard enthalpy of formation ($$\Delta H_{f}$$) is a measure of the energy change that occurs when one mole of a substance is formed from its constituent elements in their standard states. By definition, the standard enthalpy of formation is zero for elements in their standard states. In this article, we will explore which substances have $$\Delta H_{f} = 0 , \text{kJ/mol}$$ by definition.

What is the Standard Enthalpy of Formation? The standard enthalpy of formation is a measure of the energy change that occurs when one mole of a substance is formed from its constituent elements in their standard states. It is defined as the enthalpy change that occurs when one mole of a substance is formed from its constituent elements in their standard states, under standard conditions of temperature and pressure.

Which Substances Have $$\Delta H_{f} = 0 , \text{kJ/mol}$$ by Definition? By definition, the standard enthalpy of formation is zero for elements in their standard states. This means that the energy change that occurs when one mole of an element is formed from its constituent elements in their standard states is zero.

Elements in Their Standard States Elements in their standard states have a standard enthalpy of formation of zero. This is because the energy change that occurs when one mole of an element is formed from its constituent elements in their standard states is zero.

Examples of Elements with $$\Delta H_{f} = 0 , \text{kJ/mol}$$ Some examples of elements with $$\Delta H_{f} = 0 , \text{kJ/mol}$$ include:

Oxygen (O2(g)): Oxygen is an element in its standard state, and therefore has a standard enthalpy of formation of zero.
Nitrogen (N2(g)): Nitrogen is an element in its standard state, and therefore has a standard enthalpy of formation of zero.
Helium (He(g)): Helium is an element in its standard state, and therefore has a standard enthalpy of formation of zero.
Iron (Fe(s)): Iron is an element in its standard state, and therefore has a standard enthalpy of formation of zero.

Substances with Non-Zero $$\Delta H_{f}$$ Not all substances have a standard enthalpy of formation of zero. Substances that are formed from elements in their standard states, but are not in their standard states themselves, have a non-zero standard enthalpy of formation.

Examples of Substances with Non-Zero $$\Delta H_{f}$$ Some examples of substances with non-zero standard enthalpy of formation include:

Water (H2O(l)): Water is formed from hydrogen and oxygen, which are both elements in their standard states. However, water is not in its standard state, and therefore has a non-zero standard enthalpy of formation.
Bromine (Br2(l)): Bromine is formed from bromine atoms, which are not in their standard state. Therefore, bromine has a non-zero standard enthalpy of formation.

Conclusion In conclusion, the standard enthalpy of formation is a measure of the energy change that occurs when one mole of a substance is formed from its constituent elements in their standard states. By definition, the standard enthalpy of formation is zero for elements in their standard states. This means that the energy change that occurs when one mole of an element is formed from its constituent elements in their standard states is zero.

Frequently Asked Questions

Q: What is the standard enthalpy of formation?

A: The standard enthalpy of formation is a measure of the energy change that occurs when one mole of a substance is formed from its constituent elements in their standard states.

Q: Which substances have $$\Delta H_{f} = 0 , \text{kJ/mol}$$ by definition?

A: Elements in their standard states have a standard enthalpy of formation of zero.

Q: What are some examples of elements with $$\Delta H_{f} = 0 , \text{kJ/mol}$$?

A: Some examples of elements with $$\Delta H_{f} = 0 , \text{kJ/mol}$$ include oxygen (O2(g)), nitrogen (N2(g)), helium (He(g)), and iron (Fe(s)).

Q: What are some examples of substances with non-zero $$\Delta H_{f}$$?

A: Some examples of substances with non-zero standard enthalpy of formation include water (H2O(l)) and bromine (Br2(l)).

Q: Why is the standard enthalpy of formation important?

A: The standard enthalpy of formation is important because it provides a measure of the energy change that occurs when one mole of a substance is formed from its constituent elements in their standard states. This information is useful in a variety of applications, including chemistry and engineering.