Chapter 6: Thermochemistry Flashcards
Energy
The capacity to do work or to produce heat
Law of Conservation of Energy
Energy can be converted from one form to another but can be neither created nor destroyed (The energy gained by the surroundings must be equal to the energy lost by the system.)
Potential energy
Energy due to position or composition
Kinetic energy
Energy due to the motion of the object and depends on the mass of the object and its velocity (KE = 1/2 x m x v^2)
Heat
The transfer of energy between two objects due to a temperature difference
Work
Force acting over a distance
Pathway
The specific conditions that determine how energy transfer is divided between work and heat
State function (property)
A property that is independent of the pathway
e.g.: Energy change, internal energy, pressure, volume, enthalpy
System
Part of the universe on which we wish to focus attention
Surroundings
Everything else in the universe
Exothermic
Energy flows out of the system
Endothermic
Energy flows into the system
Thermodynamics
The study of energy and its interconversions
The First Law of Thermodynamics
The energy of the universe is constant
Internal energy
The sum of the kinetic and potential energies of all the “particles” in the system
Change in internal energy
∆E = q + w E = internal energy q = heat w = work
When q is positive…
A quantity of energy flows into the system via heat (an endothermic process)
When q is negative…
A quantity of energy flows out of the system via heat (an exothermic process)
When w is positive…
The surroundings do work on the system (energy flows into the system)
When w is negative…
The system does work on the surroundings (energy flows out of the system)
Work equation
Compression: Work = P x A x ∆h = P∆V
Expansion: Work = -P∆V
Enthalpy
H = E + PV H = enthalpy E = internal energy of the system P = pressure of the system V = volume of the system
At constant pressure (where only PV work is allowed)…
The change in enthalpy ∆H of the system is equal to the energy flow as heat q (Heat of reaction = change in enthalpy)
Enthalpy change equation
∆H = Hproducts - Hreactants
When ∆H is positive…
The products of a reaction have a greater enthalpy than the reactants, so heat will be absorbed by the system (ENDOTHERMIC)
When ∆H is negative…
The reactants of a reaction have a greater enthalpy than the products, so heat will be generated by the system (EXOTHERMIC)
Calorimeter
The device used experimentally to determine the heat associated with a chemical reaction
Calorimetry
The science of measuring heat based on observing the temperature change when a body absorbs or discharges energy as heat
Heat capacity
C = heat absorbed / increase in temperature
Specific heat capacity
The energy required to raise the temperature of one gram of a substance by one degree Celsius
Molar heat capacity
The energy required to raise the temperature of one mole of a substance by one degree Celsius
Energy (as heat) equation
q = s x m x ∆T s = specific heat capacity m = mass of solution ∆T = increase in temperature
Constant volume calorimetry equation
q = s x ∆T s = specific heat capacity of the calorimeter
Hess’s Law
In going from a particular set of reactants to a particular set of products, the change in enthalpy is the same whether the reaction takes place in one step or in a series of steps
Standard enthalpy of formation (∆H˚f)
The change in enthalpy that accompanies the formation of 1 mole of a compound from its elements with all substances in their standard states
Law of Summation of Heats of Formation
∆H˚reaction = sum of the heats of formation for the products multiplied by their coefficients in a balanced chemical equation - sum of the heats of formation for the reactants multiplied by their coefficients in a balanced chemical equation
Fossil fuels
Coal, petroleum, or natrual gas
Petroleum
A thick, dark liquid composed mostly of compounds called hydrocarbons that contain carbon and hydrogen
Natural gas
Usually associated with petroleum deposits, consists mostly of methane, but it also contains significant amounts of ethane, propane, and butane
Coal
Formed from the remains of plants that were buried and subjected to high pressure and heat over long periods of time
Greenhouse effect
A warming effect exerted by the earth’s atmosphere (particularly CO2 and H2O) due to thermal energy retained by absorption of infrared radiation
Syngas
Synthetic gas, a mixture of carbon monoxide and hydrogen, obtained by coal gasification
