1211K Chapter 6 & 18 Thermochemistry

Thermochemistry

The study of heat and energy in chemical reactions

Energy

The capacity to do work (w) or transfer heat (q)

Mechanical Energy

Due to the motion or position of an object

Kinetic Energy

Energy of Motion

Potential Energy

Energy related to position

Joule

The SI unit of work, heat, and energy

• Equivalent to 1 kg m² S^-2

• 1 liter-atmosphere is equal to 101.325 ____

• 1 calorie is equal to 4.184 ____

• 1 calorie (nutritional) is equal to 1000 calories or 4184 ____

System

Some component of the universe you’ve chosen to consider

Surroundings

Everything but the system

Universe

Everything

Open system

Both matter and energy can be exchanged between the system and surroundings 

Closed system

Energy, not matter, can be exchanged between the system and surroundings

Isolated system

Neither energy nor matter can be exchanged between the system and surroundings

Work

The result of a force acting through a distance— a kind of energy transfer in which the particles of the system undergo coordinated motion in a nonrandom direction

Heat

The result of thermal energy— a kind of energy transfer in which the particles of the system undergo random motion

Positive

Work done on the system by the surroundings is _____

Heat Transferred to the system from the surroundings is _____

Negative

Work done by the system on the surroundings is ______

Heat transferred from the system to the surroundings is ______

Internal Energy

U or E, the sum of the kinetic and potential energies of all particles within a system

First Law of Thermodynamics

1. The total energy of the universe is constant

2. Energy is neither created nor destroyed

3. All changes in internal energy are due to heat and/or work

Delta U

A change in internal energy is denoted:

State Function

Values are only dependent on the state of the system, not the path travelled

Path Functions

Quantities whose values depend on the path or process taken between 2 states (initial and final)

PV work

L-atm

The work done on a gas to compress it or done by the gas as it expands

Enthalpy

H = U + PV

The change in which is equal to the heat of reaction at a constant pressure

Exothermic

Energy is released from the system into the surroundings

Endothermic

Energy is absorbed from the surroundings into the system

Specific Heat

The amount of heat required to raise the temperature of 1 gram of a substance by 1 degree Celsius

q = mcdeltaT

Molar Heat Capacity

The heat required to raise the temperature of 1 mole of a substance by 1 degree Celcius

q = nCdeltaT

Heat Capacity

q = CdeltaT

Calorimetry

A lab technique for quantifying heat transfer by measuring temperature changes in substances involved

• Based on a heat balance of the system and surrounding

Heat Balance

q_system = -q_surroundings = -C_surroundings DeltaT

Surroundings

The heat evolved or absorbed by the system is determined by measuring the temperature change in the _________

Constant-pressure Calorimetry

Involves running a reaction in an insulated vessel under atm. In this situation, the heat absorbed or released by the reaction (q) is equal to the enthalpy change (deltaH)

• Happens in aqueous solution

• System is the submicroscopic reactant and product molecules

• Surroundings is the reaction solution itself

Thermochemical equation

A balanced chemical equation that also includes the enthalpy change or heat of reaction for 1 mole of reaction events of the equation as written

Heat of Reaction

The amount of heat absorbed or released during a chemical reaction, measured at constant pressure.

• DHrxn = Hprod - Hreact

Hess’s Law

The total enthalpy change of a reaction is the same, no matter how the reaction is carried out — in one step or in a series of steps

• Delta H is the same regardless of the path followed from R —> P

• Enthalpy is the sum of enthalpies of the individual steps

Standard Enthalpy of Formation

The enthalpy change for the formation reaction of an element or
compound occurring under standard conditions

• Delta H_f^o

Spontaneous

A __________ Process occurs without continuing outside influence

Entropy

(S) A measure of energy and matter dispersal in a system

Second law of thermodynamics

Spontaneous processes are associated with an increase (or no charge) in the entropy of the universe S_univ

Infinitesimal entropy change

(dS) the infinitesimal heat transferred to or from the system reversibly Sq_rev divided by the temperature T at which this heat transfer occurs:

dS = δq_rev/T

Energy per temperature

The units of Entropy are _____ ___ _________, most commonly J/K