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Energy of State Changes

Part of the Energy, Rates and Equilibrium section of Coddy's Chemistry journey. Lesson 13 of 35.

Stronger forces between particles: more energy to melt or boil. Water ( $40.7\ \mathrm{kJ/mol}$ , hydrogen bonds) against methane (about $8\ \mathrm{kJ/mol}$ , London forces).

A full heating: add the parts.

$Q = m \times c \times (T_2 - T_1) + n \times \Delta H$

Keep the units straight: J for warming, kJ for state changes.

Challenge

A cook heats $18\ \mathrm{g}$ of water ( $1\ \mathrm{mol}$ ) from $293\ \mathrm{K}$ to its boiling point, $373\ \mathrm{K}$ , and then boils all of it away. Water's specific heat is $4.18\ \mathrm{J/(g·K)}$ and boiling takes $40.7\ \mathrm{kJ/mol}$ . How much energy $Q$ , in kJ, does that take?

Try it yourself

Physics diagram: beaker

Solve for $Q$

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Energy, Rates and Equilibrium

1Energy in Reactions

Exothermic and Endothermic Energy Diagrams Enthalpy Change Activation Energy Recap - Hand Warmer

4Rates of Reaction

Collision Theory Concentration and Rate Temperature and Rate Surface Area Catalysts Recap - Speed Trials

7Practice Problems

Recap - Methanol Plant Recap - Butane Lighter Recap - Limestone Kiln

2Bond Energies

Breaking and Making Bonds Delta H from Bond Energies Hess's Law Energy and Moles Recap - Fuel Value

5Equilibrium

Reversible Reactions Dynamic Equilibrium The Equilibrium Constant Writing K Solids and Liquids in K Recap - K Builder

3Changes of State

Heating Curves Melting and BoilingEnergy of State ChangesRecap - Ice to Steam

6Changing an Equilibrium

Le Chatelier's Principle Changing Concentration Changing Pressure Changing Temperature The Haber Process Recap - Factory Settings