DP1 Chemistry - Energetics

Thermochemistry

the study of energy changes associated with chemical reactions

Temperature

measure of the average kinetic energy of the particles

Heat

the transfer of thermal energy between 2 bodies at different temps. (heat flow, heat absorbed, heat released, heat evolved.

System

The area of interest

Surroundings

The rest of the Universe outside of the system

Universe

the combination of the item under investigation and the immediate factors that can influence it.

Open (system)

System can exchange mass and energy with the surroundings, usually in the form of heat

Closed (system)

System can exchange energy with the surrounding

Isolated (system)

System does NOT allow mass or energy transfer with surroundings

Enthalpy (∆H)

the total energy of a system, some of which is stored as chemical PE in the chemical bonds

+∆H

Endothermic (feels cold)

-∆H

Exothermic (feels hot)

Bond Breaking...

Requires energy (endothermic)

Bond Forming

Releases energy (exothermic)

ΔH =

H(products) - H(reactants)

Exothermic

Heat from system is released to the surrounding.

Endothermic

Heat from the surrounding is absorbed by the system

Calorimetry

The T of a liquid inside a well insulated container (calorimeter) is measured before and after a reaction.

Specific Heat Capacity

the amount of energy required to raise the T of one gram of a substance by one degree Celsius (or Kelvin)

Heat Capacity

the amount of energy required to raise the T of a particular substance (like a thermos or styrofoam cup) one degree Celsius (or K) (versus specific heat) (Includes grams)

Standard Enthalpy Change of Formation

The enthalpy change when one mole of a compound is formed from its elements in their standard states at 298K and 1 atm pressure (SATP)

ΔHfθ for an element in its standard (most stable) state

= 0 kJ/mol.

Standard Enthalpy Change of Combustion

The energy released when one mole of a compound is burned in excess oxygen.

Hess's Law

The total ΔH for converting reactants to products is constant, regardless of the way in which the change occurs.

Bond Enthalpy

The amount of energy required to break a particular bond in one mole of GASEOUS molecules.

Lattice Enthalpy U or ΔH(lattice)

the energy required to completely separate one mole of solid ionic compound into gaseous ions.

Lattice enthalpy is related to...

Coulomb's Law (atomic charge/atomic radius)

Ionization Energy

The energy needed to remove one or more electrons from a neutral atom to form a positively charged ion is a physical property that influences the chemical behavior of the atom.

Electron Affinity

the energy given off when a neutral atom in the gas phase gains an extra electron to form a negatively charged ion.

Atomization (Diatomic)

molecules into one mole of gaseous atoms (if diatomic), or the energy required to change one mole of soli

Atomization (Not Diatomic)

the energy required to change one mole of solid atoms into one mole of gaseous atoms

Hydration

a measure of the energy released when attractions are set up between positive or negative ions and water molecules

Solution

enthalpy change when 1 mole of an ionic substance dissolves in water to give a solution of infinite dilution (you can keep dissolving solid into it)

Entropy

the measure of randomness in a system.

Entropy increase in a system can come from...

mixing different types of particles

changing state (space b/w particles) (large influence on entropy)

increase movement of particles (temperature)

increase total number of particles (increase in total # of gas particles has greater influence than any other factor)

Entropy Change

ΔS = ΣΔS(products) - ΣΔS(reactants)

+ΔS

Entropy increase

-ΔS

Entropy decrease

Standard Entropy Change, ΔSθ

the entropy change at standard conditions

Spontaneous Process

a reaction that occurs under a given set of conditions without external assistance.

Gibbs Free Energy (ΔG)

the amount of energy from that system available to do useful work

ΔGf =

ΣΔG(products) - ΣΔG(reactants)

ΔH is found experimentally through...

q=mcΔt (Δt in K or C)

ΔH is found through enthalpy of formation by...

Σ(products) - Σ(reactants)

ΔH is found through enthalpy of combustion by...

Σ(reactants) - Σ(products)

ΔH is found through bond enthalpy by...

Broken(R) - Formed(P)