Test 5 Flashcards
eqn for work
force * distance
eqn for PV work & what happens when pressure = constant
w = -P∆V w = 0 when pressure is constant
what type of energy do chem bonds have
potential
x cal = how many Cal
1000
1st law of thermodynamics
smth gains E when smth loses it
define system
chemicals in a rxn
define surroundings
the environment around the chemicals
define exothermic
system loses E, surroundings gain it
def endothermic
system gains E, surroundings lose it
define ∆V
change in volume: V₂ - V₁
define ∆T
change in temp: T₂ - T₁
define ∆E
all internal system E: w + q (work + heat)
define ∆H
enthalpy of a rxn; change in enthalpy = heat of rxn
eqn for heat transfer enthalpy @ constant pressure
∆H = qₚ
exothermic rxn x 4
heat E = product A + B → C + D + Heat E Reactant E > Product E q, ∆E, ∆H = all negative heat transferred to surroundings
endothermic rxn x 4
heat E = reactant A + B + heat E → C + D Reactant E < Product E q, ∆E, ∆H = all positive heat transferred to system
is ∆H intensive or extensive
extensive
units to write ∆H in
±kJ/x mol (write the + or - out, I swear to god)
enthalpy of formation rxn, how to write & what it is
∆Hբ
forming 1 mol of substance from elements in products in standard conditions
define specific heat capacity and units used for it, plus one extra thing about it
amt heat needed to raise temp of 1 g substance by 1° C
units in J/(g * °C)
super high for water
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)
divide J/g, bc specific heat capacity is in J/gC
Hess’s Law x 3
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
how to show work for hess’s law combination rule, 4 steps
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
standard conditions for thermochem
25°C, 1 atm
def kinetic & potential E
kinetic = E of moving object potential = stored E
liquid → gas
vaporization
gas → solid
deposition
2 rules for when ∆Hᵣₓₙ ≠ ∆Hբ of product
1) when 1+ mol of substance is being created in product
2) when reactants aren’t in their regular state of matter
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?”
qₛᵤᵣᵣ = m * Cₛ * ∆T
heat gained/lost in J = mass * specific heat * temp change in °C
what does a bomb calorimeter measure and thru what
combustion rxns; constant-volume type (?)
def calorimeter heat capacity for bomb calorimeter
AKA calorimeter constant
qₛᵤᵣᵣ in kJ = (kJ/°C)(Tբᵢₙₐₗ)
relation between qₛᵧₛ and qₛᵤᵣᵣ
-qₛᵤᵣᵣ = qₛᵧₛ
how to find ∆Hₛᵧₛ from qₛᵧₛ
∆Hₛᵧₛ = qₛᵧₛ/mol comp. used in rxn
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.”
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
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.”
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
what is a coffee cup calorimeter like x 3
constant-pressure
not air-tight
water surrounding temp measured
heat of formation formula
∆Hᵣₓₙ = Σn∆Hբ(products) - Σn∆Hբ(reactants)
n = balanced rxn coefficients
basically sum of heat enthalpy products - h. e. reactants
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
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
heat needed to convert 10g ice @ 20°C into 110°C steam?
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
when changing states but not temps, what number do you use for s → l and l → s?
fusion
when changing states but not temps, what number do you use for g → l and l → g?
vaporization
