Thermochemistry and Entropy

Flashcards covering key concepts from thermochemistry and entropy.

Thermochemistry

The study of the changes in heat associated with chemical reactions.

Exothermic Reactions

Chemical reactions that release heat.

Endothermic Reactions

Chemical reactions that absorb heat.

Enthalpy (H)

A quantity that represents the heat content of a system, equal to the internal energy plus the product of pressure and volume.

∆H (Enthalpy Change)

The amount of energy (heat) absorbed or released during a process at constant temperature.

Second Law of Thermodynamics

In a spontaneous process, there is always an increase in the entropy of the universe.

Entropy (∆S)

A measure of the degree of randomness of energy or disorder in a system.

Endothermic Reaction Example

A reaction involving an instant cold pack that absorbs heat from the surroundings.

Exothermic Reaction Example

Combustion of propane, where heat is released as a product.

Standard Enthalpy Change (∆Ho)

Enthalpy change measured when both reactants and products are in their standard states.

Process of Increasing Entropy

Occurs when a solid changes to a liquid or gas, or when more substance is produced.

Calorimetry

The study of the flow and measurement of heat

Heat Capacity

An objects amount of heat(J) needed to raise the temperature of an object by 1 degree C

Specific Heat

the heat capacity of 1 g of a substance

q

heat measurement in calorimeter

qrxn

heat transfer in reaction

qsur

heat transfer in surroundings

m

mass of water

C

specific heat of water (4.184 J/g degrees C)

Delta T

T(f) - T(i)

qrxn = ?

-qsur , heat transfer is equal in magnitude but opposite in sign to heat absorbed by surroundings

specific heat def

Heat capacity is the amount of heat required to raise the temperature of a substance by 1 °C or 1 °K

heat capacity formula

C = q/T

specific heat unit

J/degree C

specific heat capacity def

the amount of heat required to raise the temperature of one gram of a substance by 1°C or 1 °K

specific heat capacity formula

c=q/m*T

specific heat formula units

J/g deg C

determining heat of a reaction step 1

Calculate qsur (qsur= m*C*T)

determining heat of a reaction step 2

switch the sign of qsur (=qrxn)

determining heat of a reaction step 3

convert g in the question to mol

determining heat of a reaction step 4

delta H = qrxn/ mol (to get kJ)