Enthalpy
Definition
Enthalpy is a measure of total energy in a thermodynamic system. It includes internal energy which can be used for work and volume expansion against an external pressure.
Analogy
Imagine you have a piggy bank full of coins (internal energy) and bills (volume expansion). The total value inside your piggy bank represents enthalpy - all potential money you could use for buying things or investing.
Related terms
Entropy: A measure of disorder or randomness in a system. If we scatter all coins and bills from your piggy bank on your bed, entropy increases because there’s more disorder now!
Gibbs Free Energy: Represents available energy to do work at constant temperature and pressure. It's like counting only those coins from your piggy bank which are not pennies – this gives you real spending power!
Internal Energy: The total kinetic and potential energies associated with random motion of molecules within a system; it's like the total amount of coins and bills in your piggy bank.
"Enthalpy" appears in:
Study guides (7)
AP Chemistry - 6.1 Endothermic and Exothermic Processes
AP Chemistry - 6.2 Energy Diagrams of Reactions
AP Chemistry - 6.6 Introduction to Enthalpy of Reaction
AP Chemistry - 7.6 Properties of the Equilibrium Constant
AP Chemistry - 7.14 Free Energy of Dissolution
AP Chemistry - 9.2 Absolute Entropy and Entropy Change
AP Chemistry - 9.9 Cell Potential Under Nonstandard Conditions
Practice Questions (13)
What is the symbol for enthalpy?
When enthalpy is positive, what can be said about the reaction?
When enthalpy is negative, what can be said about the reaction?
In which phase change is enthalpy decreasing?
In which phase change is enthalpy increasing?
What's enthalpy?
Enthalpy is a measure of
Which law helped us understand that enthalpy was a state function (pathway independent)?
Which of the following statements is true about the relationship between entropy and enthalpy in a reaction?
The enthalpy of change for the reaction 2NH3 → N2 + 3H2 is +92 kJ/mol. The enthalpy of change for the reaction 2H2O → 2H2 + O2 is +572 kJ/mol. The enthalpy of change for the reaction N2 + O2 → 2NO is -180 kJ/mol. What is the enthalpy change for the reaction: 4NH3 + 5O2 → 4NO + 6H2O?
The enthalpy of change for the reaction S (s) + O2 (g) → SO2 (g) is -296.0 kJ/mol. The enthalpy of change for the reaction 2SO2 (g) + O2(g) → 2SO3 (g) is -198.2 kJ/mol. What is the enthalpy of change for the reaction S (s) + 3/2 O2 (g) → SO3 (g)?
The enthalpy of change for the reaction H2(g) + 1/2 O2(g) → H2O (g) is -71.2 kJ/mol. The enthalpy of change for the reaction C2H2(g) + 2H2(g) → C2H6(g) is -94.5 kJ/mol. The enthalpy of change for the reaction C2H6(g) + 7/2 O2(g) → 2CO2(g) + 3H2O(g) is -283 kJ/mol. What is the enthalpy of change for the reaction 4CO2(g) + 2H2O(g) → 2C2H2(g) + 5O2(g)?
The enthalpy changes for the formation of aluminum oxide and iron (III) oxide are 2Al(s) + 3/2 O2(g) → Al2O3(s) ΔH° -1676 kJ/mol and 2Fe(s) +3/2 O2(g) → Fe2O3(s) ΔH° -824 kJ/mol. What is the ΔH° for the reaction Fe2O3(s) + 2Al(s) → Al2O3(s) + 2Fe(s)?
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