What is the standard enthalpy change of formation (ΔHf°) for elements in their s
Practice Questions
Q1
What is the standard enthalpy change of formation (ΔHf°) for elements in their standard state?
0 kJ/mol
1 kJ/mol
ΔHf° is always positive
ΔHf° is always negative
Questions & Step-by-Step Solutions
What is the standard enthalpy change of formation (ΔHf°) for elements in their standard state?
Step 1: Understand what 'standard enthalpy change of formation' means. It is the energy change when one mole of a compound is formed from its elements in their standard states.
Step 2: Recognize what 'standard state' means. The standard state of an element is its most stable form at 1 atmosphere of pressure and a specified temperature (usually 25°C).
Step 3: Identify the elements in their standard state. For example, oxygen is O2 gas, and carbon is solid graphite.
Step 4: Learn that the standard enthalpy change of formation for any element in its standard state is defined to be 0 kJ/mol. This is a reference point for measuring the enthalpy changes of compounds.
