Thermochemistry

Question 1

isolated system

Answer 1

cannot exchange energy (heat and work) or matter with the surroundings

Question 2

closed

Answer 2

system can exchange energy (heat and work) but not matter with the surroundings

Question 3

open

Answer 3

system can exchange both energy (heat and work) and matter with the surroundings

Question 4

first law of thermodynamics

Answer 4

deltaU = Q - W

U: internal energy of the system
Q: heat added to the system
W: work done by system

Question 5

isothermal process

Answer 5

• systems temp is constant
• when deltaU is 0, like this case, the
  Q = W

Question 6

adiabatic process

Answer 6

• occurs when no heat is exchanged between the system and the environment, thus thermal energy of the system is constant throughout the process
• common bc temp and pressure control are easy
• Q = 0
• deltaU = -W

Question 7

isobaric process

Answer 7

• pressure of the system is constant
• common bc temp and pressure control are easy

Question 8

isovolumetric (isochoric) process

Answer 8

• experience no change in volume
• W = 0
• deltaU = Q

Question 9

critical point

Answer 9

boundary between liquid and gas phases

no distinction between the two

Question 10

supercritical fluid

Answer 10

results from the passage of the critical point

Question 11

endothermic

Answer 11

deltaQ > 0

Question 12

exothermic

Answer 12

deltaQ < 0

Question 13

conversion between cal and joule

Answer 13

1 cal = 4.184 J

Question 14

enthalpy deltaH

Answer 14

• equivalent to Q heat under constant pressure

Question 15

calculating heat absorbed or lost

Answer 15

q = mc • deltaT

Question 16

specific heat

Answer 16

• the amount of energy requires to raise the temp of one gram of a substance by one degree
• water specific heat is 1 (cal/g•K)

Question 17

heat capacities

Answer 17

mass • specific heat

Question 18

constant-pressure calorimeter

Answer 18

an insulated container covered w a lid and filled with a solution in which a rxn or some physical process is occurring

Question 19

bomb calorimeter (decomposition vessel)

Answer 19

• type of constant-volume calorimeter
• material is placed in steel decomp vessel which is then almost filled with pure oxygen gas
• then placed in an insulated container holding a known mass of water
• contents electrically ignited
• material combusts
• delta V = 0 and thus W = 0

Question 20

bomb calorimeter thermodynamics

Answer 20

deltaUsys = -deltaUsurr
qsys = -qsurr

Question 21

enthalpy (H)

Answer 21

change in enthalpy is equal to heat transferred into or out of rxn

deltaH = Hproducts - H reactants

positive, endothermic
neg, exothermic

Question 22

standard enthalpy of formation

Answer 22

enthalpy required to produce one mole of a compound from its elements in their standard states

298K and 1 atm

Question 23

Hess’s Law

Answer 23

deltaH = deltaH1 + deltaH2 + deltaH3

Question 24

deltaH°rxn

Answer 24

deltaH°rxn = ξdeltaHbonds broken - ξdeltaHbonds formed

considering bond enthalpy

Question 25

deltaS

Answer 25

deltaS = Qrev/T

measure of spontaneous dispersal of energy at specific temp and how much energy is spread out

deltaSuni = deltaSsys + deltaSsurr > 0

Question 26

standard entropy change for a rxn

Answer 26

deltaS°rxn = ξdeltaS°fproducts - ξdeltaS°freactants