Chapter 5

Question 1

thermodynamics

Answer 1

the study of energy and its transformations

Question 2

thermochemistry

Answer 2

• the study of the relation between chemical reactions and changes in energy
  
  • chemical rxns: energy transferred as heat

Question 3

heat(q)

Answer 3

• the energy transferred between objects because of a difference in their temperatures
• not a state function

Question 4

thermal equilibrium

Answer 4

a condition in which temperature is the same throughout a material and no further energy transfer occurs

Question 5

work(w)

Answer 5

• the energy required to move(cause motion) an object through a given distance
• work is a form of energy
  
  • work = Force x distance
• not a state function
  
  • w = -PΔV
• work done by the system leads to an increase in the system’s volume AND transfers energy to the surroundings

Question 6

potential energy (PE)

Answer 6

• the energy stored in an object because of its position
• on a moecular level:
  
  • chemical bonds and differential electric charges cause interactions btwn particles that give rise to PE
  • temperature governs motion

Question 7

state function

Answer 7

• a property based solely on a current chemical and/or physical state
  
  • it is independent of the path followed to acquire PE
    
    • ΔH and ΔE are state functions (also T,V,etc)
  • depends only on difference btwn initial and final states

Question 8

kinetic energy(KE)

Answer 8

• KE depends on mass and velocity
  
  • velocity depends on temp too so KE depends on temp
• the energy of an object in motion due to its mass and speed
  
  • KE = 1/2(m)(u)^​2
  • u=speed
• KE on a molcular level
  
  • as temp increases, avg. KE increases

Question 9

thermal energy

Answer 9

• the KE associated with the total random motion of molecules
• thermal energy is proportional to temp
• thermal energy depends on # of particles in a sample
  
  • more molcules = more themal energy if temp is constant

Question 10

electrostatic potential energy (E_el)

Answer 10

• the energy a particle has b/c of its electrostatic charge and its position w/ respect to another particle
• E_el is proportional to (Q₁ x Q₂)/d
  
  • d = distance btwn two particles
  • Q₁ and Q₂ = charge of each particle
• postive E_el = particles repel
• negative E_el = particles attract
• A lower electrostatic PE (a more negative E_el) indicates greater stability
• total energy always = KE due to random motion of particles + PE due to particle arrangment

Question 11

energy(E)

Answer 11

• the ability to do work and/or transfer heat
• the energy given off/absorbed during a rxn is equal to the difference in the energy of the reactants and the products
  
  • positive = absorbed?
  • negative = released?
• energy ca be used to do work, transfer heat

Question 12

system

Answer 12

• the specific part of the universe we are studying
  
  • often a chemical rxn or physical process

Question 13

surroundings

Answer 13

• everything that is not part of the system

Question 14

isolated system

Answer 14

• a system that exchanges neither energy nor matter with the surroundings
  
  • a thermos of hot soup with the lid screwed on tightly

Question 15

closed system

Answer 15

• a system that exchanges energy, but NOT matter with the surroundings
  
  • a cup of hot soup with a lid
    
    • heat goes out
• most real systems we deal with are closed b/c they are easier to model quantitatively

Question 16

open system

Answer 16

• a system that exchanges both energy and matter with the surrooundings
  
  • an open cup of hot soup
    
    • matter goes out as steam
    • matter goes in as crackers cheese and pepper
    • heat goes out
• cells, organisms, and Earth are all open

Question 17

exothermic process

Answer 17

• energy flows from system to surroundings
• q is negative

Question 18

endothermic

Answer 18

• energy flows from surroundings into system
• q is positive

Question 19

internal energy(E)

Answer 19

• E = KE of all components system + PE of system
  
  • not possible to determine exact values
• ΔE= E_final - E_initial
  • _​a state function b/c ΔE depends only on the initial and final states….how the change occurs in the system doesn’t matter
• doing work on a system adds to its internal energy
• total increase of the internal energy of a closed system
  
  • ΔE = q+w

Question 20

first law of thermodynamics

Answer 20

• essentially the law of conservation of energy
• The energy (ΔE=q+w) gained or lost by a system must equal the energy gained or lost by the surroundings
  
  • ΔE_sys+ΔE_surr=0
• when work is done by a system on its surroundings, internal energy of system decreases
• pressure-volume work(P-V work):
  
  • the work associated with the expansion or compression of a gas
  • when the pressure on a system remains constant but the volume of the system changes
    
    • a hot air balloon- heating the balloon causes volume to increase even though atmospheric pressure remains constant

Question 21

calorie(cal)

Answer 21

the amount of energy necessary to raise the temp of 1 gram of water by 1˚C

Question 22

joule(J)

Answer 22

• the SI unit of energy
• 4.184 J = 1 cal

Question 23

enthalpy change (ΔH)

Answer 23

• the heat absorbed by an endothermic process or given off by an exothermic process occurring at constant pressure
  
  • ΔH = q_p = ΔE + PΔV
    
    • q_p = enthalpy change at constant pressure
• ΔH<0 when energy flows out of a system and q<0
• ΔH>0 when energy flows into a system and q>0

Question 24

enthalpy(H)

Answer 24

• ΔH is defined as heat transferred at constant pressure
  
  • ΔH>0 = endothermic
  • ΔH<0 = exothermic
• the sum of the internal energy and the pressure-volume product
  
  • H = E + PV
    
    • difficult to calculate so we use ΔH
• unit is J or J/g or J/mol
• ΔH and ΔE represent changes in a state function of a system

Question 25

difference between ΔE and ΔH

Answer 25

* ΔE includes *all* the energy(heat and work) exchanged the sys with the surr * ΔE = q + w * ΔH is *only* q, the heat, exchanged at constant pressure * ΔH = q_p * ΔE and ΔH are very similar with constant volumes

Question 26

molar heat capacity (c_p)

Answer 26

* the quantity of energy required to raise the temp of 1 mole of a substance by 1˚C at constant pressure * q = nc_pΔT * ΔT is in Celsius * units = J/mol˚C

Question 27

specific heat(c_s)

Answer 27

* the quantity of energy required to raise the temp of 1 gram of a substane by 1˚C at constant pressure * units = J/g˚C

Question 28

molar enthalpy of fusion(ΔH_fus)

Answer 28

* the energy required to convert 1 mole of a solid substance at its melting point into the liquid state * Ex: the energy absorved as snow melts * q = nΔH_fus

Question 29

molar enthalpy of vaporization (ΔH_vap)

Answer 29

* the energy required to convert 1 mole of a liquid substance at its boiling point to the gas/vapor state * q = nΔH_vap

Question 30

calorimetry

Answer 30

* the measurement of the quantity of energy transferred during a physical change or chemical process * **calorimeter:** device used to measure absorption or release of energy by a physical change/chem process * assume a **closed system** * heat from sys = heat to surr * q_sys + q_cal =0

Question 31

enthalpy of reaction(ΔH_rxn)

Answer 31

* used to quantify the (heat) energy absorbed or given off by a chemical reaction under constant pressure * * aka heat of reaction * ΔH_rxn\<0 when exothermic aka heat is released * exiting system and going into surroundings * ΔH_rxn\>0 when endothermic aka heat is absorbed * entering system from the surroundings

Question 32

thermochemical equation

Answer 32

the chemical equation of a reaction that includes the change in enthalpy that accompanies that reaction

Question 33

heat capacity(C_p)

Answer 33

* the quantity of energy needed to raise the temperature of an object by 1˚C at constant pressure * referred to as a calorimeter constant (C_cal) * this value is unique to every calorimeter so units are NEVER J/g˚C or J/mol˚C * units=J/˚C * q_calorimeter=C_calorimeterΔT * we can then use q_cal to calculate quantities of energy produced * q_cal = -ΔH_rxn

Question 34

Hess's law

Answer 34

* the principle that the enthalpy or reaction(ΔH_rxn) for a reaction that is the sum of two or more reactions is equal to the sum of the ΔH_rxn values of the constituent reactions * ΔH is a state function, so we can... * 1) multiply the coefficients by a common factor * 2) reverse the rxn if we flip the sign of ΔH * Hess's law works b/c enthalpy is a state function * for a particular set of reactants and products, the enthalpy change is the same regardless of how many steps the rxn took

Question 35

standard enthalpy of formation(ΔH˚_f)

Answer 35

* the enthalphy change of a **formation rxn** * **​formation rxn:** when 1 mole of a substance is formed from its constituent elemtns in their standard states * aka [standard] heat of formation * formation reaction DOES NOT EQUAL real life synthesis

Question 36

standard conditions+states

Answer 36

* indicated by the ˚ in ΔH˚_f, **standard** **conditions** are 1 atm, usually 25˚C, and 1M concentration * **standard states:** the most stable form of a substance under standard conditions * a pure element in its most stable form under standard conditions has ΔH˚_f = 0

Question 37

standard enthalpy of reaction(ΔH˚_rxn)

Answer 37

* the energy associated with a rxn that takes place under standard conditions * aka standard heat of rxn

Question 38

phase changes

Answer 38