Chapter 10 Energy and Energy changes

Question 1

thermochemistry

Answer 1

the study of energy and energy transfer in chemical processes

Question 2

energy

Answer 2

the capacity to do work

Question 3

work

Answer 3

a force acting through a distance

Question 4

pontential energy

Answer 4

stored energy, gravitational potential energy, chemical bonds.

Question 5

kinetic energy

Answer 5

energy of motion

Question 6

system

Answer 6

the portion of universe of interest

Question 7

surrounding

Answer 7

the rest of the universe not part of the system

Question 8

temperature

Answer 8

a measure of the average kinetic energy

Question 9

thermal energy

Answer 9

the internal energy present in a system due to its molecular motion

Question 10

heat

Answer 10

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

Question 11

endothermic

Answer 11

heat is absorbed by the system

Question 12

exothermic

Answer 12

heat is released by the system

Question 13

Si Units

Answer 13

Joule, J

Question 14

Calorie

Answer 14

the energy required to raise exactly 1 g H2O by 1ºC

1cal=1000cal
1cal=1kcal
1cal=4.184 j

Question 15

types of system

Answer 15

characterized by transfer between system and surrounding

Question 16

state function

Answer 16

a value or variable that only depends on the state of the system not how it achieved that state

Question 17

internal energy, E

Answer 17

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.

Question 18

Change internal energy, ∆E

Answer 18

its is difficult to measure E so ∆E is measured

Question 19

first law of thermodynamics

Answer 19

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.

Question 20

1 last applied

Answer 20

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

Question 21

changes in internal energy

Answer 21

the change in internal energy occurs via two forms:

1.heat(q) 2.work(w)

∆E=q+w

Question 22

heat

Answer 22

+q=system gains/absorbs thermal energy

-q= system loses/releases thermal energy

Question 23

work

Answer 23

+w=work is done on the system
-w=work is done by the system

pressure-volume

Question 24

P-V work

Answer 24

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

Question 25

constants volume work

Answer 25

if the reaction is carried in a sealed container the volume is fixed

∆V=0 w=-P∆V=0J

therefore, the total change in internal energy at constant volume is:

∆E=q+w. ∆E=q+0 ∆E=qw

Question 26

enthalpy

Answer 26

often reactions are carried out under constant pressure; not constant volume

∆E=q+w ∆E=qp+(-P∆V)

rearranging, qp=∆E+P∆V, this is defined as enthalpy H: qp=∆H

Question 27

enthalpy H

Answer 27

for a system, enthalpy is the sum of the internal energy plus the pressure times volume

∆H>0 endothermic: heat flows into the system
∆H<0 exothermic:heat flows out of the system

Question 28

Stoichiometry of ∆H

Answer 28

when ∆H is given for a reaction, it is related to the moles shown in the balanced reaction.

Question 29

Calorimetry

Answer 29

the study of heat change in chemical reactions. when a system absorbs heat, there is a change in temperature

experimental it is observed: the change in temperature depends on the amount of heat absorbed

qα∆T

Question 30

heat capacity, c

Answer 30

the constant of proportionality that relates the temperature change to the heat absorbed

Question 31

heat capacity (of a system)

Answer 31

the quantity of heat required to change temperature of a system by 1ºC

q=C•∆T

the heat capacity depend on the amount of matter present in the system and is report for the system

Question 32

specific heat capacity, Cs

Answer 32

the amount of energy required to raise the temperature of 1 gram of substance by 1ºC

q=m•Cs•∆T

Question 33

molar heat capacity, Cm

Answer 33

the amount go energy required to raise the temperature of 1 mole of substance by 1ºC

Cm=J/mol ºC

Question 34

constant pressure calorimetry

Answer 34

often reaction are conducted at constant pressure, not constant volume

∆Hrxn=qrxn/nreactant

Question 35

thermochemical equation

Answer 35

chemical equation that shoes the enthalpy change in addition to the balanced species

Question 36

Manipulating ∆H

Answer 36

1. if a reaction is multiplied by n, the ∆His also multiplied by n
2. if a reaction is reversed, the sign on ∆H is changed
3. if a chemical equation can be expressed as the sum of a series of steps, then the ∆Hrxn for the overall reaction is the sum of the individual ∆Hs

Question 37

Standard states for enthalpy

Answer 37

a. for a gas the pure gat as a pressure of exactly 1 atm
b. for liquid or solid the pure substance in its most stables from at a pressure of 1 atm and temperature of interest
c. for substance in solution the substance in solution at a concentration of exactly 1 M

Question 38

Standard enthalpy change, ∆H

Answer 38

the change in enthalpy for a process when all reactants and products are in their standard states

Question 39

standard enthalpy of formation,∆Hfº

Answer 39

for a pure compound the change in enthalpy when 1 mole of the compound is formed from its constituent elements in their standard states

Question 40

standard enthalpy of reaction, ∆Hºrxn

Answer 40

the ∆Hfº provides the energy of each substance, therefore for a reaction the ∆Hrxn is given by:

∆Hºrxn= ∑nproduct∆Hfºproduct-∑nreactant∆Hfºreactant
n=number of moles

Question 41

bond enthalpies, ∆HBE

Answer 41

the energy required to break 1 mole of the bond for the gas phase species. Also known as bond dissociation energy