Download HONORS CHEMISTRY STUDY GUIDE Thermochemistry

HONORS CHEMISTRY STUDY GUIDE
Thermochemistry
-Know what thermochemistry is.
-Know that energy is stored in chemical bonds as chemical potential energy.
-Know what energy is.
-Know the definition of and symbol for heat (q).
-Be able to define system and surroundings.
-Know that the total energy in the universe is constant: Law of Conservation of Energy
-Know what an exothermic and endothermic reaction is and be able to identify them
Know the associated sign for ΔH and how it appears in a thermochemical equation.
-Know units for heat: joule, calorie and Calorie
Be able to convert between them: 1 cal. = 4.184j
1000 cal = 1 Cal
-Know the definition of and difference between heat capacity and specific heat
- Know the symbol for specific heat (c).
-Understand that specific heat represents how much energy is needed to change the temperature of a
substance.
-Know how to calculate specific heat given mass, heat, and temperature change:
q = mcΔT
q = heat (j)
m = mass (g)
c = specific heat
ΔT = change in temp.
-Be able to rearrange the above equation to solve for any variable, given the other three.
-Know what enthalpy (H) and change in enthalpy (ΔH) is.
-Know that ΔH = qsystem
-Know what calorimetry is.
-Know the two types of calorimeters, constant pressure and constant volume and when you would use
each
-Know that in calorimetry you are measuring the qsurroundings (heat taken in or given off by the water) and
that from that knowledge we know that qsystem = -qsurroundings. Flip the sign.
-Be able to solve q=mcΔT equations involving calorimetry: Both one step and 2 step types
In two step equations: use the calorimetry data to get qsys, then uses that value to
solve q=mcΔT for the unknown.
-Understand how to write a thermochemical equation and what it tells you.
-Know how to write the heat of reaction (ΔHrxn) and what it tells you
specifically, be able to convert a thermochemical equation to a regular equation plus a ΔHrxn.
-Know how to figure out heat of reaction per mole of any reactant or product
(Divide total heat of reaction by molar coefficient in front of that particular chemical species).
-Know what a standard heat of formation (ΔHf)is.
-Be able to calculate heat of reaction from (ΔHf) of the reactants and the products.
ΔHf = Σ ΔHf products- = Σ ΔHf reactants
- Understand how heat works in changes of state
heat can either raise an object’s temperature or change its state, not both.
-Know what heat of vaporization and condensation are.
-Know what heat of fusion and solidification are.
-Know that to calculate the change of state of a substance you use the following:
number of moles (n) X ΔH(vap or fusion) (in kj).
-Know to calculate a change of temperature in a substance you use: q = mcΔT (in j).
-Be familiar with a heating curve and be able to identify the states of matter in every section
as well as the names of the heats associated with the phase changes sections.
-Be able to do problems determining the heat where the temperature and phase of a substance
changes.
-Understand that in such problems each section of the heat curve needs its own calculation.
The total heat can then be determined by adding the heat associated with each
temperature or phase change.
Heat Curve for 1 mol of water (below):
Temp
E
100 oC
D
C
0 oC
B
A
Heat 
-Know how to use Hess’s law to use know equations to find the ΔH for of an unknown equation from
related known equation.
-Know the definition of entropy (S) and be able to calculate ΔS for a reaction from standard entropies (on
chart).
-Know that reactions want to give off energy (exothermic, -ΔH) and become more disorder (positive
entropy (ΔS)).
-Know that a reaction’s spontaneity is determined by Gibbs Free Energy (ΔG) and that a negative Δ –G
indicates a spontaneous reaction.
-Be able to calculate ΔG from ΔH and ΔS : ΔG = ΔH – TΔS (Temperature in K)
-Understand how temperature effects the spontaneity of a reaction.