Chapter 5 Flashcards
energy
capacity to do work/transfer heat
thermodynamics
study of energy and transformations (chemical, mechanical, electrical, etc.)
thermochemistry
relationships b/w chemical reactions and energy changes that involve heat
Potential energy- from position
electrostatic potential energy
interactions b/w charged particles
E(el) =
(kQ1Q2) / d
- Q1/Q2 = electrical charges (2 charge particles)
- d = distance
- k = 8.99 x 10^9 J (m/c^2)
- 1 J = 1 kg m^2/s^2
1st law of thermodynamics
energy can be converted from 1 form to another but it is neither created nor destroyed
making bonds
releases energy
breaking bonds
consumes energy
system
portion we single out to study
open system
exchange heat and mass w/ surroundings
closed system
only exchange heat (not mass) w/ surroundings
isolated system
doesn’t exchange heat or mass w/ surroundings
internal energy
sum of all kinetic and potential energy of system
∆E =
Change in E
∆E = E(final) – E(initial)
∆E = q + w
(+) = E(final) > E(initial)
System gained/absorbed energy from surrounding
(-) = E(final)) < E(initial)
System lost energy to surrounding
q=
sum of heat added to/liberated from system
- (+) = system gains heat
- (-) = systems loses heat
w=
work done on/by system
- (+) = work is done on system
- (-) = work is done by system
endothermic
system absorbs heat from surroundings
- ∆H = (+)
exothermic
system releases heat into surrounds
- ∆H = (-)
state functions
we only care about start & end points; not how we got there
work
chemical or physical energy –> mechanical work w/ change in volume
pressure-volume work; W=
W = -P∆V
∆V = V(initial)-V(final)
enthalpy (H); ∆H
heat at constant pressure
- ∆H = ∆E + P∆V
∆H = (+)
system gained heat = endothermic
∆H = (-)
system released heat = exothermic
∆H(rxn)=
H(products) = H(reactants)
calorimetry
measurement of heat of flow (∆H)
calorimeter
device to measure heat flow
qsolution =
(msolution)( ∆T)(Cs) = -qrxn
bomb calorimetry; qrxn =
qrxn = Ccal x ∆T
- Ccal = constant (bomb only)
heat capacity (C)
energy to raise temp of object 1 d K (1 d C)
Specific heat capacity Cs=
heat capacity of 1 gram of substance
- Cs = q / (m x ∆T)
Molar heat capacity (Cm)
heat capacity of 1 mole of substance
Specific quantity
known mass m of substance gains/loses heat
Hess’s Law: ∆Hrxn =
∆Hrxn = sum of ∆H for each step
enthalpies of formation (∆Hf)
∆Hf = (n)(∆H)(Hproducts) - (m)(∆H)Hreactants
bond enthalpy
∆H for breaking of a particular bond in 1 mole of gaseous substance
fuel value
energy released when 1 g food in combusted
