The enthalpy of formation, denoted as $\Delta H_f^\circ$, is the change in enthalpy when one mole of a compound is formed from its constituent elements in their standard states. Standard state conditions are 298 K (25°C) and 1 atm pressure. Understanding and applying Hess's Law using standard enthalpies of formation allows for the calculation of enthalpy changes for reactions, which is a critical skill for AP Chemistry. This worksheet will provide interactive practice to solidify your understanding.
Match the terms on the left with their definitions on the right:
| Term | Definition |
|---|---|
| 1. Standard Enthalpy of Formation | A. The energy required to break one mole of bonds in the gaseous phase. |
| 2. Hess's Law | B. The enthalpy change for a reaction is the sum of the enthalpies of formation of the products minus the sum of the enthalpies of formation of the reactants. |
| 3. Bond Energy | C. The enthalpy change when one mole of a compound is formed from its elements in their standard states. |
| 4. Standard State | D. A defined set of conditions (298 K and 1 atm) used for measurements. |
| 5. Enthalpy Change of Reaction | E. The overall change in enthalpy during a chemical reaction. |
Match them up! (Answers are hidden, think it through!)
Complete the paragraph below using the following words: products, reactants, formation, Hess's Law, standard.
The enthalpy change of a reaction can be calculated using __________ and the enthalpies of __________. According to __________ , the overall enthalpy change is equal to the sum of the enthalpies of formation of the __________ minus the sum of the enthalpies of __________.
Explain why the enthalpy of formation of an element in its standard state is always zero. Give an example. 🌎
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