THERMOCHEMISTRY
The Nature & Types of Energy
Nuclear Energy
- The energy sorted within the collection of neutrons and protons in the atom
- The fusion reaction in the sun provides our planet with all the energy it needs
Electrical Energy
- The energy associated with the value flow of electrons
- Batteries
Chemical Energy
- The energy sorted within the bonds of chemical substances
- Petroleum
Thermal Energy
- The energy associated with the random motion of atoms and molecules
- A cup of hot water
Potential Energy
- The energy available by virtue of an object's position
- Water that behind a dam
Law of Conservation Energy
- Total energy of an isolated system remains constant
- Water can produce electricity
Kinetic Energy
- The energy that it possesses due to its motion
- An asteroid falling towards Earth is very large
Energy Changes in Chemical Reactions
Thermochemistry
- The study of heat change in chemical reaction
System
- The study of heat change in chemical reactions
- The specific part of the universe that is of interest in study
Surroundings
- Freely allows both energy and matter to be transferred in and out of a system
- The rest of the universe outside the system
Example System & Surroundings
https://www.chem.fsu.edu/chemlab/chm1020lmanual/exp14/systemsurr.gif
Temperature
- Measure of the thermal energy
- TEMPERATURE ≠ THERMAL ENERGY
Heat
- The transfer of thermal energy between two bodies that are different temperature
Systems
Closed Systems
- No reactants or products can escape, only heat can be exchanged freely
Isolated Systems
- Cannot transfer energy or matter with its surroundings
Exothermic Process
- Process that gives off heat-transfer thermal energy from the system to the surroundings
Endothermic Process
- Process in which heat has to be supplied to the system from the surroundings.
Enthalpy (H)
- Used to quantity the heat flow into or out of and systemin a process that occurs at constant pressure
- ∆H = H (products) - H (reactans)
- ∆H = heat given off absorbed during a reaction at constant pressure
Calorimetry
- The specific heat (s) of a substance is the amount of heat (q) required to raise the temperature of 1g of a substance by 1℃
- The heat capacity (C) of a substance is the amount of heat (q) required to raise the temperature of a given quantity (m) of the substance by 1℃
- C = ms
Constant-Volume Calorimetry
- qsys = qwater + qbomb + qrxn
- qsys = 0
- qrxn = -(qwater + qbomb)
qwater = ms∆t
qbomb = Cbomb∆t
Reaction at Constant V
∆H ≠ qrxn
∆H ∿ qrxn
Constant-Pressure Calorimetry
- qsys = qwater + qcal + qrxn
- qsys = 0
- qrxn = -(qwater + qcal)
qwater = ms∆t
qcal = Ccal∆t
Reaction at Constant P
∆H = qrxn
Standard Enthalpy of Formation & Reaction
- Establish an arbitrary scale with the standard enthalpy of formation (∆H⁰f) as a reference point for all enthalpy expressions
- Standard enthalpy of formation (∆H⁰f) is the heat change that results when 1 mole of a compound is formed from its elements at a pressure of 1 atm
The standard enthalpy of reaction (∆H⁰rxn) is the enthalpy of a reaction carried out at 1 atm
- aA + bB → cC + dD
- ∆H⁰rxn = [c∆H⁰f (C) + d∆H⁰f (D)] - [a∆H⁰f(A) + b∆H⁰f (B)]
- ∆H⁰rxn = ∑n∆H⁰f (products) - ∑m∆H⁰f (reactats)
Hess's Law
- When reactants are converted to products, the changes in enthalpy is the same whether the reaction takes place in one step or in a series of steps.
- (Enthalpy is a state function. It doesn't matter how to get there, only where it start and end)