Assignment 7 Flashcards
phase change
breaking IMFS
chemical reaction
breaking bonds
making a bond (energy)
gives off
breaking a bond (energy)
costs energy
ΔH
enthalpy of reaction change in heat of a system found by heat of formation ΔH = Ef - Ei = Hproducts - Hreactants
Ef
final energy (product’s energy)
Ei
initial energy (reactant’s energy)
exothermic
gives off energy, ΔH is negative, reaction gets hot
endothermic
takes (absorbs) energy, ΔH is positive, reaction gets cold
Q (J)
transferred heat Q = mCpΔT m - mass (g) Cp - heat capacity (J/gK or J/gC) ΔT - change in heat (Tf - Ti) (C or K)
heat capacity (Cp)
the heat needed to change the temp of 1g by 1degC (1K)
unique to each substance and state
related to IMFs
calorie
ener needed to increase temp of 1g by 1degC
heat of fusion (hf)
IMF term, unique to each substance
Q = mhf
m - mass
hf - heat of fusion
heat of vaporization (hv)
unique to each substance
Q = mhv
m - mass
hv - heat of fusion
is there a temp change during a state change
no, because the energy is going into increasing the KE of the particles, so they can change state, not into heating up the substance
Hess’s Law
the heat of reactions is the algebraic sum of the subreactions
Qrxn = Q1 + Q2 + Q3…
ΔHrxn = ΔH1 + ΔH2 + ΔH3…
enthalpy
heat an object or substance contains
heat or enthalpy of formation (ΔHf)
combination of 2 or more elements to form a non-elemental product
used in lieu of bond energy
heat gained from the formation of the elements
if you have a question where a substance goes through a phase change, then
you solve for each step of the phase change with the Q equations and add up all the answers Q = mCpsolidΔT Q = mhf Q = mCpliquidΔT Q = mhv PV = nRT
finding enthalpy using heat of formation
given the molecular equations, do a system of equations until you reach the final equation
gibbs free energy (ΔG)
ΔG = ΔH - (TΔS)
entropy
how much the energy:temp ratio changes in a system
free energy
measure of imbalance of energy
ΔG = 0
equalibrium
forward and reverse equations are spontaneous
ΔG is negative
extra energy
spontaneous with free energy
ΔG is positive
need energy
non-spontaneous
