THERMOCHEMISTRY

The Nature & Types of Energy

Nuclear Energy

  • The energy sorted within the collection of neutrons and protons in the atom
  • The fusion reaction in the sun provides our planet with all the energy it needs

Electrical Energy

  • The energy associated with the value flow of electrons
  • Batteries

Chemical Energy

  • The energy sorted within the bonds of chemical substances
  • Petroleum

Thermal Energy

  • The energy associated with the random motion of atoms and molecules
  • A cup of hot water

Potential Energy

  • The energy available by virtue of an object's position
  • Water that behind a dam

Law of Conservation Energy

  • Total energy of an isolated system remains constant
  • Water can produce electricity

Kinetic Energy

  • The energy that it possesses due to its motion
  • An asteroid falling towards Earth is very large

Energy Changes in Chemical Reactions

Thermochemistry

  • The study of heat change in chemical reaction

System

  • The study of heat change in chemical reactions
  • The specific part of the universe that is of interest in study

Surroundings

  • Freely allows both energy and matter to be transferred in and out of a system
  • The rest of the universe outside the system

Example System & Surroundings
https://www.chem.fsu.edu/chemlab/chm1020lmanual/exp14/systemsurr.gif

Temperature

  • Measure of the thermal energy
  • TEMPERATURE ≠ THERMAL ENERGY

Heat

  • The transfer of thermal energy between two bodies that are different temperature

Systems

Closed Systems

  • No reactants or products can escape, only heat can be exchanged freely

Isolated Systems

  • Cannot transfer energy or matter with its surroundings

Exothermic Process

  • Process that gives off heat-transfer thermal energy from the system to the surroundings

Endothermic Process

  • Process in which heat has to be supplied to the system from the surroundings.

Example
https://www.thoughtco.com/thmb/LC9VMDICnwzLlDS9bUzWoGroMRM=/3000x2000/filters:fill(auto,1)/endothermic-and-exothermic-reactions-602105_final-c4fdc462eb654ed09b542da86fd447e2.png

Enthalpy (H)

  • Used to quantity the heat flow into or out of and systemin a process that occurs at constant pressure
  • H = H (products) - H (reactans)
  • H = heat given off absorbed during a reaction at constant pressure

Calorimetry

  • The specific heat (s) of a substance is the amount of heat (q) required to raise the temperature of 1g of a substance by 1℃
  • The heat capacity (C) of a substance is the amount of heat (q) required to raise the temperature of a given quantity (m) of the substance by 1℃
  • C = ms

Constant-Volume Calorimetry

  • qsys = qwater + qbomb + qrxn
  • qsys = 0
  • qrxn = -(qwater + qbomb)
  • qwater = ms∆t


    qbomb = Cbomb∆t


  • Reaction at Constant V


    ∆Hqrxn


    ∆Hqrxn

Constant-Pressure Calorimetry

  • qsys = qwater + qcal + qrxn
  • qsys = 0
  • qrxn = -(qwater + qcal)
  • qwater = ms∆t


    qcal = Ccal∆t


  • Reaction at Constant P


    ∆H = qrxn

Standard Enthalpy of Formation & Reaction

  • Establish an arbitrary scale with the standard enthalpy of formation (∆H⁰f) as a reference point for all enthalpy expressions
  • Standard enthalpy of formation (∆H⁰f) is the heat change that results when 1 mole of a compound is formed from its elements at a pressure of 1 atm

The standard enthalpy of reaction (∆H⁰rxn) is the enthalpy of a reaction carried out at 1 atm

  • aA + bB → cC + dD
  • ∆H⁰rxn = [c∆H⁰f (C) + d∆H⁰f (D)] - [a∆H⁰f(A) + b∆H⁰f (B)]
  • ∆H⁰rxn = ∑n∆H⁰f (products) - ∑m∆H⁰f (reactats)

Hess's Law

  • When reactants are converted to products, the changes in enthalpy is the same whether the reaction takes place in one step or in a series of steps.
  • (Enthalpy is a state function. It doesn't matter how to get there, only where it start and end)