Chemistry - Ch 5 Flashcards
Thermodynamics
the study of energy and its transformations; from Greek therme dynamis (heat power)
Thermochemistry
energy changes involving heat
Energy
the capacity to do work or to transfer heat
Work
the energy used to cause an object with mass to move against a force; w = force times distance
Heat
the energy used to cause the temperature of an object to increase; energy transferred from a hotter object to a colder one
Kinetic energy
the energy of motion; Ek = 1/2 mass times volume squared
Potential energy
arises when a force operates on an object by virtue of its position relative to other objects; Ep = mass times gravitational constant (9.8m per second squared) times height of the object relative to some reference height
Force
any kind of push or pull exerted on an object; F = mass times gravitational constant, 9.8m/s^2
Electrostatic potential energy
arises from the interactions between charged particles; Eel = k (constant of proportionality = 8.99 x 10^9 J-m/C^2 times the electrical charge on the two interacting objects, Q1 & Q2) divided by the distance separating them
Joule
SI unit for energy; 1 J = 1kg-m^2/s
calorie
non SI unit; =4.184 J; not the same as the nutritional Calorie (capitalized); 1 Cal = 1000 cal = 1kcal
System
the portion of the universe we single out for study; may be open, closed, or isolated
Surroundings
everything else that is not the system
Closed system
can exchange energy but not matter with its surroundings
Isolated system
one in which neither energy nor matter can be exchanged with its surroundings (ex. insulated thermos)
First Law of Thermodynamics
Energy is conserved; it can neither be created nor destroyed
Internal energy
sum of all the kinetic and potential energies of all its components
Change in internal energy
Delta E = E final - E initial; positive answer = system has gained energy from its surroundings; negative = system has lost energy to its surroundings; Delta E = q (heat added to or liberated from the system) plus w (work done on or by the system)
Endothermic
when a process occurs in which the system absorbs heat (endo = into)
Exothermic
process in which the system loses heat (exo = out of)
State function
a property of a system that is determined by specifying the system’s condition or state, in terms of temperature, pressure, etc.; the value of a state function depends only on the present state of the system, not on the path the system took to reach that state
Pressure-volume work (P-V work)
the work involved in the expansion or compression of gases (w = - P times the change in volume of the system)
Enthalpy
thermodynamic function that accounts for heat flow in processes occurring at constant pressure when no forms of work are performed other than P-V work; from the Greek, enthalpein, “to warm”); H (enthalpy) = E (internal energy) plus pressure times volume; a state function; extensive property
Change in enthalpy
change in internal energy plus the product of the constant pressure times the change in volume (Delta H = Delta E + P times Delta V); heat gained or lost at constant pressure
Enthalpy of reaction (heat of reaction)
enthalpy change that accompanies a reaction
Thermochemical equations
balanced chemical equations that show the associated enthalpy change
The enthalpy change for a reaction is ____ in magnitude but ____ in sign to the change in enthalpy for the reverse reaction
equal; opposite
Calorimetry
the measurement of heat flow
Calorimeter
a device used to measure heat flow
Heat capacity
the temperature change experienced by an object when it absorbs a certain amount of heat; the heat capacity of an object is the amount of heat required to raise its temperature by 1K (or 1 degree Celsius)
Molar heat capacity
the heat capacity of one mole of a substance (Cm)
Specific heat capacity (specific heat)
the heat capacity of one gram of a substance (Cs); = quantity of heat transferred divided by (grams of substance times temperature change)
Bomb calorimeter
device used to measure heat accompanying combustion reactions at constant volume
Radiation
direct loss of heat from the body to cooler surroundings
Convection
heat loss by virtue of heating air that is in contact with the body
Evaporation
cooling that occurs when perspiration is generated at the skin surface by the sweat glands
Hess’s Law
if a reaction is carried out in a series of steps, the change in enthalpy for the overall reaction will equal the sum of the enthalpy changes for the individual steps
Enthalpies of vaporization
change in enthalpy for converting liquids to gases
Enthalpies of fusion
change in enthalpy for melting solids
Enthalpies of combustion
change in enthalpy for combusting a substance in oxygen
Enthalpy of formation (heat of formation)
enthalpy change associated with the process of forming a compound from its constituent elements
Standard state
defined set of conditions; pure form at atmospheric pressure
Standard enthalpy change
enthalpy change when all reactants and products are in their standard state
Temperature of interest
usually 298 K (25 degrees C)
Standard enthalpy of formation
change in enthalpy for the reaction that forms one mole of the compound from its elements, with all substances in their standard states; standard enthalpy of formation of the most stable form of any element is zero b/c there is no formation reaction needed when the element is already in its standard state
Fuel value
energy released when one gram of a material is combusted
Fossil fuels
coal, petroleum, and natural gas; world’s major sources of energy
Natural gas
consists of gaseous hydrocarbons (compounds of hydrogen and carbon); primarily methane, with small amounts of ethane, propane, and butane
Petroleum
liquid composed of hundreds of compounds, most of which are hydrocarbons, with the remainder being chiefly organic compounds containing sulfur, nitrogen, or oxygen
Coal
solid; contains hydrocarbons of high molecular weight as well as compounds containing sulfur, oxygen, or nitrogen
Renewable energy
energy sources that are essentially inexhaustible
