Chapter 10 Energy and Energy changes Flashcards
thermochemistry
the study of energy and energy transfer in chemical processes
energy
the capacity to do work
work
a force acting through a distance
pontential energy
stored energy, gravitational potential energy, chemical bonds.
kinetic energy
energy of motion
system
the portion of universe of interest
surrounding
the rest of the universe not part of the system
temperature
a measure of the average kinetic energy
thermal energy
the internal energy present in a system due to its molecular motion
heat
the transfer of thermal energy due to differences in temperature
heat moves from a region of higher temperature to a region of lower temperature
the process of heat flow is defined with repeat to the system
endothermic
heat is absorbed by the system
exothermic
heat is released by the system
Si Units
Joule, J
Calorie
the energy required to raise exactly 1 g H2O by 1ºC
1cal=1000cal
1cal=1kcal
1cal=4.184 j
types of system
characterized by transfer between system and surrounding
state function
a value or variable that only depends on the state of the system not how it achieved that state
internal energy, E
the sum of all the kinetic and potential energy within a system
E is a state function
E is based on parameters such as temperature, pressure, concentration, phase, etc.
Change internal energy, ∆E
its is difficult to measure E so ∆E is measured
first law of thermodynamics
in chemical processes, energy is neither created nor destroyed. the total energy of the universe is constant in all processes, the change in energy of the universe is zero.
1 last applied
if energy cannot be crated nor destroyed…t=the energy lost by a system must be the same amount gained by the surrounding. The energy gained by a system must be the same amount lost by the surroundings
∆Esystem=-∆Esurrounding
∆Esystem+∆Esurrounding=0
changes in internal energy
the change in internal energy occurs via two forms:
1.heat(q) 2.work(w)
∆E=q+w
heat
+q=system gains/absorbs thermal energy
-q= system loses/releases thermal energy
work
+w=work is done on the system
-w=work is done by the system
pressure-volume
P-V work
work as a result of a volume change agains an external pressure
w=-P∆V
P:exnternal Pressure, atm
∆V: change in volume
∆V: Vfinal-Vintial
for expansions Vf>Vi work is done by the system w<0
for contraction Vf0