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–The study of the heat flow that accompanies chemical reactions.
Define Energy and heat in thermochemistry
Energy–The capacity to do work
Heat–A particular form of energy that is transferred from a body at a high temperature to one at a lower temperature when they are brought into contact with each other
Define Kinetic energy
Kinetic energy is energy of motion or energy that is being transferred.
Define Thermal energy.
Thermal energy is the energy associated with temperature. Thermal energy is a form of kinetic energy
What is ΔX?
X Final - X inital
Is heat flow a state property?
–Heat flow is NOT a state property!! It depends on how the process is carried out
Heat is given the symbol q.
When is q negative or positive?
- –q is positive when heat flows into the system from the surroundings
- –q is negative when heat flows from the system into the surroundings
1 cal = _ Joules
1 kcal = _ kJ
1 food Calorie = _ Kcal
Expand the define these 2 formulas.
q = CΔt
q = mcΔt
- Q = mc∆TQ = heat energy (Joules, J)
- m = mass of a substance (kg)
- c = specific heat (units J/kg∙K)
- ∆ is a symbol meaning "the change in"∆T = change in temperature (Kelvins, K)
The formula for kinetic energy is:
1 mile is how many km?
1 pound is how many grams?
Expand these formulas for work.
- m = mass in kg
- g = gravity = 9.81 m * s ^-1
- F = force in Newtons
- w = work in joules
The formula for velocity.
v = sqaure root(2E/m)
m = meters
The ideal gas Law
PV = nRT
- P = Atm
- V= Liters
- n = moles
- R = 0.08206 for atm 8.314 for joules
- T = temperature in Kelvins
kJ to Liter * atm
(0.101 kJ=1 L⋅atm)
- p= liters * atm
- v - change in volume (Liters)
Fahrenheit to Celsius
(1.8)C + 32 = F
What is the specific heat of water?
4.184 j/g ºCelsius
Grams to moles
Moles x Molecular weight = Grams
Calorimeter to q formula.
q reaction = -c (specific heat) calorimeter Δt
qreaction = -m water X 4.18 J/(g . °C) x Δt
Formulas for enthalpy.
- –Enthalpy is a state variable
- –ΔH = Hproducts – Hreactants
qreaction = ΔH = H products – H reactants
Rules of Thermochemistry
1. The magnitude of ΔH is directly proportional to the amount of reactant or product
2. ΔH for the reaction is equal in magnitude but opposite in sign for ΔH for the reverse of the reaction
3.The value of ΔH is the same whether the reaction occurs in one step or as a series of steps This rule is a direct consequence of the fact that ΔH is a state variableThis rule is a statement of Hess’s Law
The formula for enthalpies of formation.
- –Enthalpies of Formation can be used to calculate ΔHfº for a reaction.
- –To do this, apply this general rule:
- –The standard enthalpy change, ΔHº, for a given thermochemical equation is equal to the sum of the standard enthalpies of formation of the product compounds minus the sum of the standard enthalpies of formation of the reactant compounds
ΔHº = ∑ΔHfº products - ∑ ΔHfº reactants
Note—elements can be omitted because ΔHfº = 0 for elementsΔH°f H+ (aq) = 0
Relationship between ΔH and ΔE
H = E + PV
ΔH = ΔE + Δ(PV)
- Remember the Idea gas law
- The PV product is important only where gases are involved; it is negligible when only liquids or solids are involved
- Δ(PV) = ΔngRT
- –Δng is the change in the number of moles of gas when the reaction takes place
ΔH = ΔE + ΔngRT
ΔE=q + w
- E = Joules
- q = heat
- w = work
x kJ=1 L⋅atm
0.101 kJ=1 L⋅atm