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