Thermochemistry

–The study of the heat flow that accompanies chemical reactions.

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

Kinetic energy is energy of motion or energy that is being transferred.

Thermal energy is the energy associated with temperature. Thermal energy is a form of kinetic energy

X Final - X inital

–Heat flow is NOT a state property!! It depends on how the process is carried out

• –q is positive when heat flows into the system from the surroundings
• –q is negative when heat flows from the system into the surroundings

• 4.184
• 4.184
• 1

C=heat capacity

• 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)

KE=  (1/2)m⋅v^2

• m = kg
• v = m/s

1.61km

454 grams

• m = mass in kg
• g = gravity = 9.81 m * s ^-1
• F = force in Newtons
• w = work in joules

v = sqaure root(2E/m)

m = meters

PV = nRT

• P = Atm
• V= Liters
• n = moles
• R = 0.08206 for atm 8.314 for joules
• T = temperature in Kelvins

(0.101 kJ=1 L⋅atm)

ΔE=q−PΔV

• p= liters * atm
• v - change in volume (Liters)

(1.8)C + 32 = F

4.184 j/g ºCelsius

Moles x Molecular weight = Grams

q reaction =  -c (specific heat) calorimeter Δt

qreaction = -m water X 4.18 J/(g . °C) x Δt

• –Enthalpy is a state variable
• –ΔH = Hproducts – Hreactants

qreaction = ΔH = H products – H reactants

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

• –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

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

• E = Joules
• q = heat
• w = work

0.101 kJ=1 L⋅atm