Chapter 7 Flashcards
Thermochemistry
study of the relationships between chemistry and energy
Energy
capacity to work
Work
the result of a force acting through a distance
heat
the flow of energy by a temperature difference
kinetic energy
energy associated with the motion of an object
Thermal energy
energy associated with the temperature of an object
potential energy
energy associated with the position or composition of an object
chemical energy
energy is associated with the relative positions of electrons and nuclei in atoms and molecules
law of conservation of energy
energy can be neither created nor destroyed
surrounding
everything with which the system can exchange energy
kinetic energy
1/2 mv^2
m- kg
v- m/s
kinetic energy - J
1 calories (cal) to Joules (J)
1 cal = 4.184 J
kilo watt per hour to joules
1 kWh = 3.60 x 10^6 J
thermodynamics
the general study of energy and its interconversions
first law of thermodynamics
the total energy of the universe is constant
internal energy (E)
the sum of the kinetic and potential energies of all of the particles that compose the system
The internal energy of a chemical system
delta E = E(products) - E(reactants)
Reactants have a higher internal energy than the products
delta E(sys) Is negative
-energy flows out of the system into the surroundings
reactants have a lower internal energy than the products
delta E(sys) is postive
energy flows into the system from the surroundings
Change in thermal energy of the system
heat transfer (q) + work done (w)
when q is positive
system gains thermal energy
when q is negative
system loses thermal energy
when w is positive
work down on the system
when w is negative
work done by the system
when a change in internal energy is positive
energy flows into the system
when a change in internal energy is negative
energy flows out of the system
Delta E(sys)
- delta E (surr)
higher the heat capacity of a system
smaller the change in temperature for a given amount of absorbed heat
The formula for F, W, D
Work = work as a force (F) x acting through a distance (D)
the formula for F, P, A
Force = external pressure (P ext) x Area the pressure acts on (A)
The formula for W, P, V
Work = -Pext x change in volume
Enthalpy (H)
a system as the sum of its internal energy and the product of its pressure and volume
Formula for enthalpy
H = change in E + P (change in V)
Endothermic reaction
chemical reaction with a positive H
- absorbs heat from its surroundings
- strong bonds break to form weak bonds
Exothermic reaction
chemcial reaction with a negative H
- weak bonds break to form strong bonds
standard delta H(rxn)
sum of (delta Hf products x stoichiometry) - sum of (delta Hf reactants x stoichiometry)
