Thermodynamics & Calorimetry

Collision Theory

reactants need to combine w/ enough energy and in proper orientation in order to react

effective collision

a collision that results in a chemical reaction

law of conservation of energy

energy cannot be created or destroyed

kinetic energy

energy used for motion

potential energy

stored energy- when reactants collide

activated complex

unstable phase while reaction is occurring

enthalpy

the amount of energy(heat) being stored in bonds of a compound.

Note: products & reactants almost always have an absorption release of enthalpies

endothermic reaction

• when products have a higher enthalpy

• reaction in which energy is absorbed

exothermic reaction

• reaction in which energy is released

• when products have a lower enthalpy

specific heat

substance ability to resist temperature change

high specific heat

requires a lot of energy to inc. or dec. in temperature

Calorimetry Equation

mcΔT

Q

heat (joules)

M

mass (grams) \*if not in grams, convert

C

specific heat (j/gC)

T

temperature (C)

reactants

1

products

6

activation complex

3

Heat of the reaction

5

Q of absorbed

Q of released =

Q of released

Q of absorbed =

\-Q

if energy is lost (__Q)

\+Q

if energy is absorbed (__Q)

ΔH (delta H)

change in variable

H final-H initial

\-ΔH

exothermic H

\+ΔH

endothermic H

potential energy (hold together)

there is a specific amount of energy holding together H2 & O2

potential energy

When the particles collide, Kinetic Energy becomes ______

5 things to increase rate of Effective collision

• temperature (changes energy & likelihood, speed & rate)

• pressure (decrease in volume, more collisions)

• surface area (increase # of particles for collisions)

• presence of catalyst

• concentration (likelihood of collisions is higher bc more molecules)

no, sometimes they bounce off because:

• not enough energy

• did not collide in the right spot

Do molecules always react when they collide?

they collide

why do molecules react?

entropy

the amount of disorder in a system

naturally increases (easier to create disorder than order)

least entropy

particles in solids stay in place: rigid, fixed shape, fixed volume (____entropy)

most entropy

gas particles move freely & randomly (____ entropy)

least particles

least disorder (solid)

most particles

most disorder (gas)

S

entropy

entropy equation

ΔS = S final - S initial

spontaneous

• uses energy to create reaction

• once reaction starts, continues on own

• these reactions can possibly take a long time

non spontaneous

* needs a constant source of energy

\-ΔG

spontaneous reaction

which thermic is more favorable

exothermic (more spontaneous)

which ΔS is more energetically favorable

\+ΔS

\+ΔS

inc. in entropy

\-ΔS

dec. entropy

Exothermic + inc entropy (-ΔS) =

ALWAYS SPONTANEOUS

Endothermic + dec. entropy =

NEVER SPONTANEOUS

gibbs free energy equation

ΔG = ΔH - TΔS