(9-10) Thermodynamics

Thermodynamics definition

The science of energy transfer and its effects on matter

What does thermodynamics predict

Whether a reaction will take place and energy changes but not how fast

What does kinetics predict

The rate at which a reaction proceeds

Kinetic energy definition

The energy of moving objects or mass in motion

Potential energy definition

Energy that is stored in a system

Heat definition

A form of energy caused by random molecular motion

Temperature definition

A measure of the average kinetic energy of a system

Conduction heat transfer

Heat transfer through direct contact of solid objects

Convection heat transfer

Gross movement of materials driven by density differences

Radiation heat transfer

Transfer of heat energy via electromagnetic waves

Celsius to Kelvin conversion

Add 273.15 to Celsius temperature to get Kelvin

Normal body temperature in Kelvin

310 K which is 37 degrees Celsius

Work definition thermodynamics

Energy transfer associated with ordered macroscopic motion

Work sign convention

Negative when system does work on surroundings

Heat vs Work difference

Heat involves random microscopic motion due to temperature difference

Isolated system

Exchanges neither energy nor matter with surroundings

Closed system

Exchanges energy with surroundings but not matter

Open system

Exchanges both energy and matter with surroundings

Sign convention positive

Energy transferred into the system

Sign convention negative

Energy transferred out of the system

First Law of Thermodynamics

Energy cannot be created or destroyed only transferred

Conservation of Energy

Total energy in isolated system remains constant

Seven forms of energy

Electrical gravitational chemical radiation thermal mechanical nuclear

Enthalpy definition

Heat energy change within a system expressed as delta H

Delta H positive

Endothermic reaction energy absorbed from surroundings

Delta H negative

Exothermic reaction energy released to surroundings

Crystallisation enthalpy change

Negative delta H because bonds form and energy is released

Melting enthalpy change

Positive delta H because bonds break and energy is required

Evaporation enthalpy change

Positive delta H because molecules overcome intermolecular forces

Entropy definition

Measure of randomness disorder or probability of arrangements

Second Law of Thermodynamics

Entropy of isolated system increases or stays same in spontaneous process

Entropy and disorder

Higher entropy associated with greater disorder and randomness

Entropy and molecular motion

Greater degrees of freedom in molecular motion increases entropy

Rotational motion entropy

Molecular rotation contributes to degrees of freedom

Vibrational motion entropy

Atomic vibration within molecules contributes to entropy

Temperature effect on entropy

Entropy increases with increasing temperature

Absolute zero temperature

Negative 273.15 degrees Celsius equals zero Kelvin all motion stops

Third Law of Thermodynamics

At absolute zero entropy of perfectly crystalline substance is zero

Heat capacity definition

Amount of heat needed to produce unit change in temperature

Heat capacity units

Joules per Kelvin or J per K

Heat capacity and entropy

Materials with high heat capacity have higher entropy

Gibbs Free Energy equation

Delta G equals delta H minus T delta S

Delta G negative meaning

Process is spontaneous system can do work on surroundings

Delta G positive meaning

Process is not spontaneous requires external energy input

Delta G at equilibrium

Delta G equals zero forward and reverse reactions balanced

Spontaneous reaction requirements

Negative delta H and positive delta S both favour spontaneity

Temperature effect on spontaneity

Higher temperature makes entropy term more significant TdeltaS

Endothermic spontaneous reaction

Can occur if positive delta S is large enough to overcome positive delta H

Free energy practical analogy

Free energy is like money you must spend it to do what you want

Solubility thermodynamic property

Represents maximum equilibrium concentration determined by delta G

Melting point meaning

Transition from crystalline solid to liquid state reflects bond strength

Partitioning definition

Distribution of drug between oil and aqueous phases indicates membrane permeability

Drug receptor binding

Understood through free energy changes and bond strength analysis

Heat conduction vs convection

Conduction is through solid contact while convection involves material movement

Exothermic reaction characteristics

Releases heat to surroundings has negative delta H

Endothermic reaction characteristics

Absorbs heat from surroundings has positive delta H

Thermodynamics applications pharmacy

Drug discovery disposition formulation stability receptor interactions

Protein unfolding thermodynamics

Endothermic positive delta H but spontaneous due to positive delta S

Spontaneity and time scale

Thermodynamic spontaneity does not mean reaction occurs quickly

Free expansion gas vacuum

Occurs spontaneously without heat or work exchange shows entropy drives spontaneity

Disorder probability entropy

Random arrangements more probable than ordered arrangements

Crystalline solid entropy

Lower entropy than liquid or gas due to fixed molecular positions

Gas entropy vs solid

Gas has highest entropy due to maximum molecular freedom

System reaching equilibrium

Moves toward state of lowest free energy until delta G equals zero

Ionic bonding and entropy

Formation of ionic bonds is exothermic delta H negative

Hydrogen bonding enthalpy

Formation of hydrogen bonds is exothermic delta H negative

Bond breaking energy requirement

Breaking any bond requires energy input is endothermic positive delta H

System surroundings energy

When system gains energy surroundings lose equal energy

Activation energy note

Thermodynamics does not include activation energy consideration

Reversible vs spontaneous

Spontaneous reaction not necessarily fast but favourable

Freezing point thermodynamics

Freezing is exothermic negative delta H releases heat

Melting requires energy

Melting is endothermic positive delta H requires heat input

Pharmaceutical formulation stability

Related to delta G of drug degradation negative delta G means unstable

Drug solubility prediction

Free energy change of dissolution determines solubility

Receptor binding affinity

Stronger binding correlates with more negative delta G values

Micellization thermodynamics

Micelle formation driven by negative delta G free energy decrease

Thermodynamic favorability

Negative delta G indicates thermodynamically favorable proces