Thermochemistry

• Thermochemistry

  • Study of energy changes that occur during chemical reactions and changes of state.
  • Study of heat change inchemicalreactions.​
• Thermodynamics

  • Study of the relationship between heat and the other forms of energy, particularly the transfer of heat and work.
  • A number refers to the magnitude of change.
  • Sign (+,-) indicates the direction of the flow.
• Open System

  • Transfer of energy canbe exchange between the system and the surroundings.
• Closed System

  • Only energy can be exchanged between the system and surroundings.
• Isolated System

  • Matter and energy cannot be transferred between the surround and system.
• Heat (Q)

  • Transfer of energy between a system and surroundings due to temperature difference.
  • Transfer of thermal energy between two bodies thatare at different temperatures.​
  • Energy that flows intoor out of a system because of a difference intemperature between the system and its surroundings. ​
• Work (W)

  • Force applied over a given distance.
  • Energy transfer between a system and its surroundings due to a force acting through a distance.
• Internal Energy (E)

  • Sum of the kinetic energy and potential energy of the system.
• Enthalphy (H)

  • Used to quantify the heat flow into or out of asystem in a process that occurs at constant pressure.​
  • Change in Heat = heat given off or absorbed during a reaction at constant pressure​
  • Amount of heat flow in a system with constant pressure $Qp+$
• Calorimetry

  • Science of measuring heat based on the change in temperature of an observed body when it releases or absorbs heat.
  • Measures the flow of energy (as heat) between the system and its surroundings.​
• Heat Capacity

  • Amount of heat necessary to increase the temperature of a substance by 1 Degree Celsius.
  • Amount of heat(q) required to raise the temperature of a given quantity(m)of the substance by one degree Celsius.​
• Combustion

  • Chemical Process
  • Organic compound reacts with oxygen to form carbon dioxide and water, and releases energy in the form of heat.
• Heat of Combustion

  • Amout og heat produced during combustion reaction.
• Heat of Reaction

  • Enthalpy of change for chemical equation as it is indicated.
  • value of qrequired toreturn a system to the given temperature atthe completion of the reaction.
• Hess's Law

  • Enthalpy change of an overall reaction is the sum of the enthalpy changes of individual steps.
  • Allows the determination of the heat of reaction by adding two or more thermochemical equations to give the final heat of reaction.
• Standard Heat of Reaction

  • Can be used to determine the heat of reaction indirectly.
• Molality

  • Number of moles of solute per kilogram of solvent.
• Dilution

  • Involves the addition of solvent, which decreases the concentration of the solute in the solution.
• Concentration

  • Involves the removal of solvent, which increases the concentration of the solute in the solution.
• Perfect Concentration

  • Describes the percent composition of substance in the total mass/volume of the solution.
• Energy

  • Capacity to do work
• Thermal Energy

  • Energy associated with the random motion of atoms and molecules​
• Chemical Energy

  • Energy stored within the bonds of chemical substances​
• Nuclear Energy

  • Energy stored within the collection of neutrons and protons in the atom​
• Electrical Energy

  • Energy associated with the flow of electrons​
• Potential Energy

  • Energy available by virtue of an object’s position​
• Temparature

  • Measure of the thermal energy.
• Heat (Sign q)

  +q

  • Heat is absorbed by the system.
• Heat (Sign q)

  -q

  • Heat is evolved by the system.
• Heat of Reaction:

  Exothermic Process

  • Chemical reaction or physical change in which heat is evolved (q is negative). ​
  • Out of a system
  • Transfers thermal energy from the system to thesurroundings.  ​
• Heat of Reaction:

  Endothermic Process

  • Chemical reaction or physical change in which heat is absorbed (q is positive). 
  • Into a system
  • Heat has to be supplied to the system from the surroundings.  ​
• Law of Conservation of Energy:

  Energy

  • Transferred between the system and the surroundings.​
  • Negative sign indicates the flow of energy.​
• First Law of Thermodynamics

  • When work is done, it gains energy and work denoted as positive (+w).
  • The system may also absorbs heat (+q) or releases heat to the surroundings (-q).  ​
• Specific Heat (C)

  • Amount of energy needed to increase the temperature of one gram of a substance by 1 degree Celsius. ​
  • Amount of heat (q)required to raise the temperature ofone gramof thesubstance byone degreeCelsius.​
• Thermochemical Equations

  • Chemical equation for a reaction  (including phase labels) in which the equation is given a molar interpretation, and the enthalpy of reaction for these molar amounts is written directly after the equation.                 ​
• Thermochemical Equations

  • Includes energy changes.​
  • Chemical equation that shows the value and direction of heat in a reaction.​
  • In exothermic reactions, heat is a product (it's being formed), so a reaction of this kind might look like this: A + B ---> C + D + heat ​
  • And similarly, if a reaction is endo, then it acts like a reactant (goes on the left side): ​A + B + heat ---> C + D ​
• Thermochemical Equations

  • important to note phase labels because the enthalpy change, DH, depends on the phase of the substances.               ​