Class Summary Thermochemistry (1)

SOLUTION STOICHIOMETRY

• Involves calculations dealing with the amounts of substances in chemical reactions.

CHARACTERISTICS OF ACIDS

• Acids are substances that, when dissolved in water, produce hydrogen ions (H+).

• Key reactions:

  • H+ (aq) + SO4^2- (aq) ↔ H2SO4 (aq)

  • H3PO4 (aq) dissociates to form H2PO4- (aq) and further to HPO4^2- (aq).

THERMOCHEMISTRY

• Deals with heat energy changes during chemical reactions.

  • Based on Thermodynamics, which examines heat, energy, and work relationships.

INTERNAL ENERGY

Basic Equation

• ΔE = q + w

  • ΔE: Total change in internal energy of a system.

  • q: Heat exchanged with surroundings.

  • w: Work done by/on the system.

Signs of Internal Energy

• Positive Internal Energy:

  • Heat absorbed (q > 0).

  • Work done on system (w > 0).

• Negative Internal Energy:

  • Heat released (q < 0).

  • Work done by system (w < 0).

• Isolated Systems:

  • ΔE = 0 (energy is conserved).

FIRST LAW OF THERMODYNAMICS

• ΔE(system) = -ΔE(surroundings).

• Isolated systems cannot exchange heat or work, leading to zero change in internal energy.

CHANGE IN INTERNAL ENERGY

• Decreases with heat loss or work done by the system.

• Increases with heat addition or work done on the system.

• Energy conservation: if lost by the system, it's gained by surroundings.

ENDOTHERMIC vs EXOTHERMIC REACTIONS

Exothermic Reaction

• Releases energy in the form of heat.

  • Reactants → Products + Heat

Endothermic Reaction

• Absorbs energy from surroundings as heat.

  • Reactants + Heat → Products

ENTHALPY

• ΔH = E + PV

  • E: Internal energy.

  • P: Pressure.

  • V: Volume.

REACTIONS AND HEAT CHANGES

Forward Reaction

• Converts 93.4 g of SO2 to SO3.

  • Enthalpy Change: -198.2 kJ/mol (Exothermic)

  • Releases heat, making surroundings warmer.

Reverse Reaction

• Converts SO3 back to SO2 and O2.

  • Enthalpy Change: +198.2 kJ/mol (Endothermic)

  • Absorbs heat, making surroundings cooler.