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6.3Thermochemistry

Heat Transfer and Thermal Equilibrium — AP CHEMISTRY Revision Notes & Topical Questions

5 min read 8 parts Lesson 7 of 14 1 quiz

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Lesson summary

6.3 Heat Transfer and Thermal Equilibrium — AP CHEMISTRY notes: Explain heat flow, thermal energy versus temperature, and thermal equilibrium.Heat — energy transferred because of a temperature difference, flowing from hot to coldTemperature — a measure of the average kinetic ener…

  • Bathtub and coffee cup
  • Isolated system
  • Collisions
  • Temperature — a measure of the average kinetic energy of particles
  • Two bodies at different temperatures are placed in contact
  • Heat flows from the hotter body to the colder body

Part 1 of 6Heat and temperature

Heat
  • Heat energy transferred because of a temperature difference, flowing from hot to cold
Temperature
  • Temperature a measure of the average kinetic energy of particles
Thermal energy
  • Thermal energy the total kinetic energy of all particles
  • It depends on the mass of the substance, but temperature does not.

Part 2 of 6Thermal energy versus temperature

  • Bathtub and coffee cup
    • a bathtub of water at 45 °C holds more thermal energy than a cup at 70 °C
    • The bathtub has more molecules and so more total molecular motion.

Part 3 of 6Heat transfer to equilibrium

1
Two bodies at different temperatures are placed in contact.
2
Heat flows from the hotter body to the colder body.
3
The hotter body cools while the colder body warms.
4
Heat flow stops when both are at the same temperature (thermal equilibrium).

Part 4 of 6Conservation in heat transfer

Conservation in heat transfer
Isolated system
  • Isolated system heat lost by one body equals heat gained by the other: qlost = −qgained
Example
  • Example hot iron at 200 °C in water at 25 °C warms the water and cools the iron to a common temperature

Part 5 of 6Particle-level view

Collisions
  • Collisions faster particles in the hotter body transfer kinetic energy to slower particles in the colder body
Equilibrium
  • Equilibrium at equilibrium the average kinetic energies are equal

Part 6 of 6More from the specification

1Lattice precipitation as an insoluble solid
  • Lattice precipitation as an insoluble solid exceeding ionic product thresholds drives immediate crystallization of oppositely charged ions into an insoluble solid precipitate.
2Product
  • A substance formed in a reaction.
3Lattice
  • A regular, repeating three-dimensional arrangement of particles.
4Reactants
  • The substances that react together at the start of a reaction.
5Combustion
  • Burning in oxygen
6Lattice energy
  • Enthalpy change when one mole of an ionic compound forms from its gaseous ions.
7Heating curve
  • A graph of temperature against time as a substance is heated.
8Energy diagram
  • Plot of potential energy against reaction progress.
9Cooling curve
  • A graph of temperature against time as a substance cools.
10Exothermic
  • A reaction that transfers thermal energy to the surroundings.
11Endothermic
  • A reaction that takes in thermal energy from the surroundings.
12Surroundings
  • Everything other than the reacting chemicals.
13Dissolution
  • Process of a solute dissolving in a solvent.
14Hydration
  • The addition of steam to C=C to make an alcohol.

Key terms

TermMeaning
HeatEnergy transferred due to a temperature difference.
TemperatureMeasure of average kinetic energy of particles.
Thermal energyTotal kinetic energy of the particles in a substance.
Thermal equilibriumNo net energy flow because temperatures are equal.

Avoid these mistakes

Avoid these mistakes
Saying heat flows from the body with more mass — heat flows from the higher temperature regardless of mass.
Saying cold flows into a body — only heat flows, from hot to cold.
Using temperature as a measure of total energy — thermal energy also depends on the amount of substance.

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