chapter 5 review Flashcards
system
the part of the universe chosen to study
surroundings
the rest of the universe
open systems
freely exchanges energy AND matter with its surroundings
closed system
can exchange energy, but NOT matter with is surroundings
isolated system
cannot exchange energy OR matter with its surroundings
kinetic energy
the energy of a MOVING object (includes thermal energy-molecular motion)
potential energy
energy resulting from condition, position, or composition (includes chemical energy- potential energy stored in bonds)
the first law of thermodynamics
energy can be converted from one form to another, but cannot be created or destroyed
internal energy of a system (U or E)
sum of all the potential and kinetic energies in the system
ΔU=
q (heat) + w (work)
ΔU isolated=
0
ΔU system =
-ΔU surroundings
system to surroundings
q and w (-)
surroundings to system
q and w (+)
heat
the transfer of thermal energy between a system and surroundings due to temperature difference
1 cal=
4.184 J
(P-V) pressure-volume work
work involved in the expansion or compression of gas
w (work)=
-PextΔV
negative external pressure times the change in volume
how can you tell if P-V work has happened
conceptually= change of gas in a chemical reaction
ex) 2C2H6(s) + 7O2(g) —> 6H2O(l) + 4CO2 (g)
there were 7 moles of gas and then it became four moles of gas
visually= the piston moves
heat capacity(C)=
q/ΔT
q=
mcΔT
solid to liquid
melting or fusion
liquid to gas
evaporation or vaporization
enthalpy(H)
the change in the energy of a system at constant pressure, sum of the change in internal energy and the P-V product
ΔH=
ΔU + PΔV
enthalpy is positive in an
endothermic reaction
enthalpy is negative in an
exothermic reaction
simple calorimeter
coffee cup
constant pressure
complex calorimeter
bomb calorimeter
constant volume
qcombustion=
qreaction (qrxn)
qcalorimeter=
-qrxn
qcal=
CcalΔT
heat capacity times the change in temp
standard enthalpy of formation (ΔHf)=
sum of products minus sum of reactants
standard state for C
solid graphite
standard state for H2
gas
standard state for I2
solid
standard state for S8
solid
standard state for Br2
liquid
standard state for cl2
gas
system releases energy
sign is negative
work done ON system
positive
work done BY a system
negative
lower specific heat
open to change in temp, takes less energy
higher specific heat
more resistant to change in temp, requires more energy
