Thermochemistry Summary

Chapter 6: Thermochemistry

• Chemical Hand Warmers: Utilize heat from the oxidation of iron.

  • Reaction: $4 ext{Fe}(s) + 3 ext{O}<em>2(g) \rightarrow 2 ext{Fe}</em>2 ext{O}_3(s)$
  • Exothermic reaction; temperature rise depends on hand warmer size, glove size, and heat released.

• Nature of Energy: Energy affects matter; it is the capacity to do work, defined as $ext{Energy} = ext{work} = ext{force} \times ext{distance}$.

  • Heat transfers energy due to temperature differences.

• Energy, Heat, and Work: Energy can be a property of an object or a collection of objects.

  • Heat and work: two modes of energy exchange.

• Classification of Energy:

  • Kinetic Energy: Energy of motion.
  • Thermal Energy: Energy related to temperature (form of kinetic energy).
  • Potential Energy: Stored energy associated with position or composition.
  • Chemical Energy: Related to the structure of molecules and atoms.

• Conservation of Energy:

  • Total energy remains constant; energy can only be transformed, not created or destroyed.

• System and Surroundings:

  • System: Focus of energy study; Surroundings: Everything else that energy can exchange with.
  • Energy gained/lost in the system equals energy lost/gained in surroundings.

• Kinetic Energy Calculation:

  • $ext{KE} = \frac{1}{2} mv^2$; Units: Joules (J).

• Units of Energy:

  • 1 Joule (J) = Energy to move 1 kg 1 meter.
  • 1 Calorie (cal) = Energy to raise 1 g water 1 °C.

• First Law of Thermodynamics: Energy conservation applies to chemical processes.

  • Energy changes must sum to zero in system and surroundings: $\Delta ext{Energy}<em>{universe} = 0 = \Delta E</em>{system} + \Delta E_{surroundings}$.

• Internal Energy: Sum of kinetic and potential energies in a system; change is a state function: $\Delta E = E<em>{final} - E</em>{initial}$.

• Energy in Chemical Reactions:

  • Example Reaction: $ext{C}(s) + ext{O}<em>2(g) \rightarrow ext{CO}</em>2(g)$ results in energy release; reverse reaction absorbs energy.

• Energy Flow:

  • Energy leaving a system reduces the system's energy; energy entering increases it.
  • Energy diagrams visually represent energy flow in reactions, indicating whether energy change is positive or negative.