Test 5

Question 1

eqn for work

Answer 1

force * distance

Question 2

eqn for PV work & what happens when pressure = constant

Answer 2

w = -P∆V
w = 0 when pressure is constant

Question 3

what type of energy do chem bonds have

Answer 3

potential

Question 4

x cal = how many Cal

Answer 4

1000

Question 5

1st law of thermodynamics

Answer 5

smth gains E when smth loses it

Question 6

define system

Answer 6

chemicals in a rxn

Question 7

define surroundings

Answer 7

the environment around the chemicals

Question 8

define exothermic

Answer 8

system loses E, surroundings gain it

Question 9

def endothermic

Answer 9

system gains E, surroundings lose it

Question 10

define ∆V

Answer 10

change in volume: V₂ - V₁

Question 11

define ∆T

Answer 11

change in temp: T₂ - T₁

Question 12

define ∆E

Answer 12

all internal system E: w + q (work + heat)

Question 13

define ∆H

Answer 13

enthalpy of a rxn; change in enthalpy = heat of rxn

Question 14

eqn for heat transfer enthalpy @ constant pressure

Answer 14

∆H = qₚ

Question 15

exothermic rxn x 4

Answer 15

heat E = product
A + B → C + D + Heat E
Reactant E > Product E
q, ∆E, ∆H = all negative
heat transferred to surroundings

Question 16

endothermic rxn x 4

Answer 16

heat E = reactant
A + B + heat E → C + D
Reactant E < Product E
q, ∆E, ∆H = all positive
heat transferred to system

Question 17

is ∆H intensive or extensive

Answer 17

extensive

Question 18

units to write ∆H in

Answer 18

±kJ/x mol (write the + or - out, I swear to god)

Question 19

enthalpy of formation rxn, how to write & what it is

Answer 19

∆Hբ

forming 1 mol of substance from elements in products in standard conditions

Question 20

define specific heat capacity and units used for it, plus one extra thing about it

Answer 20

amt heat needed to raise temp of 1 g substance by 1° C
units in J/(g * °C)
super high for water

Question 21

A piece of copper with a mass of 218 g has a heat capacity of 83.9 J/°C. What is the specific heat of copper? (1 step)

Answer 21

divide J/g, bc specific heat capacity is in J/gC

Question 22

Hess’s Law x 3

Answer 22

1) Bc you can combine rxn A→B and rxn B→C to make rxn A→C, you can add their ∆Hs to get overall ∆H
2) Multiply rxn coefficients and ∆H by the same factor
3) To reverse the rxn, change the sign of the ∆H

Question 23

how to show work for hess’s law combination rule, 4 steps

Answer 23

1) Write out both rxns:
A+B→C+D with ∆H = -10kJ & C+D→E+F with ∆H = -20kJ
2) Combine: 
A + B + C + D → C + D + E + F
3) Cross out what you don't need:
 A + B +  ̶C̶ ̶+̶ ̶D̶  → C̶ ̶+̶ ̶D̶  + E + F
4) Rewrite overall rxn and add ∆Hs:
A + B → E + F
-10kJ + (-20kJ) = -30kJ ∆H

Question 24

standard conditions for thermochem

Answer 24

25°C, 1 atm

Question 25

def kinetic & potential E

Answer 25

kinetic = E of moving object
potential = stored E

Question 26

liquid → gas

Answer 26

vaporization

Question 27

gas → solid

Answer 27

deposition

Question 28

2 rules for when ∆Hᵣₓₙ ≠ ∆Hբ of product

Answer 28

1) when 1+ mol of substance is being created in product

2) when reactants aren’t in their regular state of matter

Question 29

formula to solve smth like “Benzene’s specific heat capacity is 1.74 J/g·°C. If 16.7 kJ of energy is absorbed by a 225-g sample of benzene at 20.0°C, what is its final temperature?”

Answer 29

qₛᵤᵣᵣ = m * Cₛ * ∆T

heat gained/lost in J = mass * specific heat * temp change in °C

Question 30

what does a bomb calorimeter measure and thru what

Answer 30

combustion rxns; constant-volume type (?)

Question 31

def calorimeter heat capacity for bomb calorimeter

Answer 31

AKA calorimeter constant

qₛᵤᵣᵣ in kJ = (kJ/°C)(Tբᵢₙₐₗ)

Question 32

relation between qₛᵧₛ and qₛᵤᵣᵣ

Answer 32

-qₛᵤᵣᵣ = qₛᵧₛ

Question 33

how to find ∆Hₛᵧₛ from qₛᵧₛ

Answer 33

∆Hₛᵧₛ = qₛᵧₛ/mol comp. used in rxn

Question 34

how to do bomb calorimetry probs like “T rises from 25°C to 29°C in bomb calorimeter when 3.5 g sucrose combusts. Find ∆Hᵣₓₙ for sucrose combustion in kJ/mol sucrose. Heat capacity is 4.90 kJ/°C. Mol mass of sugar is 342.3 g/mol.”

Answer 34

1) find qₛᵤᵣᵣ with calorimeter constant (kJ/°C)(Tբᵢₙₐₗ)
2) get ∆H of qₛᵧₛ by reversing sign on qₛᵤᵣᵣ
3) divide qₛᵧₛ by mol of the substance used to find ∆Hₛᵧₛ

Question 35

how to do coffee cup calorimetry probs like “Two solutions, initially at 24.6°C, mix in a coffee cup calorimeter. When 100 mL of 0.1 M AgNO₃ solution mixes with 100 mL of 0.2 M NaCl solution, calorimeter T rises to 25.3°C. Find ∆H°rxn. Assume density & heat capacity of the solutions = that of water.”

Answer 35

1) find qₛᵤᵣᵣ with calorimeter constant (kJ/°C)(Tբᵢₙₐₗ)
2) get ∆H of qₛᵧₛ by reversing sign on qₛᵤᵣᵣ
3) divide qₛᵧₛ by mol of the substance used to find ∆Hₛᵧₛ

Question 36

what is a coffee cup calorimeter like x 3

Answer 36

constant-pressure
not air-tight
water surrounding temp measured

Question 37

heat of formation formula

Answer 37

∆Hᵣₓₙ = Σn∆Hբ(products) - Σn∆Hբ(reactants)
n = balanced rxn coefficients
basically sum of heat enthalpy products - h. e. reactants

Question 38

Steps for: "Solid Na2O2 reacts with liquid water to make aqueous Na2O2 and O gas. How much heat is released if 327.2 g of O gas is made from the reaction of Na2O2 and water under standard conditions?"
Substance	ΔH°f(kJ/mol)
  Na2O2(s)	–510.9  
  NaOH(aq)	–469.6  
  H2O(l)	        –285.8

Answer 38

1) balance eqn: Na2O2 + 2H2O → 2NaOH + O2
2) write out sum of product coeffs * their ΔH°fs - reactant coeffs * their ΔH°fs
3) take that number & multiply by # mol listed in the eqn

Question 39

heat needed to convert 10g ice @ 20°C into 110°C steam?

Answer 39

1) H₂O (s) @ -20°C → H₂O (s) @ 0°C
(ice at its temp now to ice at its maximum temp before turning states)
find q₁ with your specific heat eqn
2) … → H₂O (l) @ 0°C
(ice at 0°C to water at 0°C)
multiply mol H₂O by fusion heat (bc s → l) for q₂
3) … → H₂O (l) @ 100°C
(water at its temp to water at max temp before turning states)
find q₃ w/ specific heat eqn
4) …→ H₂O (g) @ 100°C
(water at 100°C to gas at 100°C)
multiply mol by vaporization heat (bc l → g) for q₄
5) …→ H₂O (g) @ 110°C
(steam @ temp now to steam at final temp)
use specific heat eqn to get q₅
6) add up q₁₋₅ to get total E

Question 40

when changing states but not temps, what number do you use for s → l and l → s?

Answer 40

fusion

Question 41

when changing states but not temps, what number do you use for g → l and l → g?

Answer 41

vaporization