AP CHEM: Thermochemistry

Exothermic

Process that releases heat into the surroundings.

Endothermic

Process that absorbs heat from the surroundings.

First law of thermodynamics

Energy is conserved; it can change form, but not be created or destroyed.

q surroundings

q system

ΔHsystem

Heat change of the system at constant pressure.

ΔHsoln

Heat change when a solute dissolves in a solvent

Specific heat

Heat needed to raise 1 g of a substance by 1 °C.

Heat capacity

Heat needed to raise an object’s temperature by 1 °C.

Hess’s Law

Total enthalpy change equals the sum of enthalpy changes for individual steps.

Standard heat of formation

Heat change when 1 mole of a compound forms from its elements in their standard states

Work

Energy transfer when a force moves an object; in chemistry, often pressure–volume work.

Kinetic energy (thermal)

Energy from particle motion; depends on temperature.

Potential energy (Chemical)

Stored energy in chemical bonds and forces.

Bond Energy

Energy required to break 1 mole of a bond in the gas phase.

Molar Heat Capacity

Heat needed to raise 1 mole of a substance by 1 °C.

Heat of Vaporization

Heat needed to convert 1 mole of liquid to gas at constant T and P.

Heat of Fusion

Heat needed to convert 1 mole of solid to liquid at constant T and P.

Calorimeter

Device that measures heat flow in chemical or physical changes.

Low potential energy=

High stability

High potential energy

Less stability

Dilution process=

(Delta H1) + (Delta H2) + (Delta H3) = DELTA H soln

Method of transfer of Energy (DELTA E)

q (heat) and w (work)

q (heat)

q= (mass)(specific heat)(final temp-initial temp)

measured in KJ

w (work)

work DONE on the system

w= -P(final volume-initial volume)

sign indicates endo vs exo work

measured in KJ or J

Heat given off by rxn vs heat absorbed by surroundings?

Heat given off (by rxn/system) = -Heat gained (by surroundings)

Cold to the touch

Endo thermic (+)

Heat evolves

(Heat is produced)

Open Container=

w= 0

No gas produced=

w= 0

Energy changes for element stages

Plateau

Phase change

thermo stoic with delta H vap, fus

Bond Enthalpies

BONDS BROKEN - BONDS FORMED= delta Hrxn

Change in Enthalpy using bond energies

AH = Bond energy of reactants - bond energy of products

Standard Enthalpy of Formation

The heat that is released or absorbed when one mole of a compound is formed from its elements in their standard states

Increasing/decreasing slope

Temperature change

q is calculated using MCAT

Phase changes

Added E is used to break Intermolecular forces/ attraction forces

Activation Energy