Unit 6: Fundamentals of Thermodynamics and Energy

System

The chemical reaction or phase change being studied in thermodynamics.

Surroundings

Everything else outside the system, including the container and the solvent.

First Law of Thermodynamics

Energy is conserved; it cannot be created or destroyed, only transferred.

Exothermic Process

A process where heat flows out of the system into the surroundings, making the surroundings hotter.

Endothermic Process

A process where heat flows into the system from the surroundings, making the surroundings cooler.

Sign Convention for Exothermic

Heat flow is negative (q < 0).

Sign Convention for Endothermic

Heat flow is positive (q > 0).

Bond Energy

The energy required to break a bond.

Enthalpy Change (ΔH)

The overall change in energy during a reaction, calculated as the difference between the energy required to break bonds and the energy released when bonds form.

Activation Energy (Ea)

The energy barrier that must be overcome for a reaction to occur.

Potential Energy Diagram

A graph that shows the energy changes during a reaction with potential energy on the y-axis and reaction coordinate on the x-axis.

Thermal Equilibrium

A state where two objects in contact reach the same temperature, and heat transfer stops.

Specific Heat Capacity (c)

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

Calorimetry

An experimental technique used to measure heat transfer.

Calorimetry Equation

q = mcΔT, used to calculate heat transfer without phase change.

Enthalpy of Fusion (ΔHfus)

The energy required to melt a solid into a liquid or freeze a liquid into a solid.

Enthalpy of Vaporization (ΔHvap)

The energy required to boil a liquid into a gas or condense a gas into a liquid.

Heating Curve

A graph that shows how temperature changes as heat is added over time, including slopes for temperature change and plateaus for phase changes.

Common Mistake about Systems

Mixing up the system and surroundings in calorimetry problems.

Energy Units Confusion

ΔH values are usually in kJ/mol, while specific heat is in Joules; conversion may be necessary.

Using q=mcΔT in Phase Changes

Incorrectly applying the specific heat formula during a phase change, where ΔT = 0.

Bond Breaking Energy Misconception

Believing that breaking bonds releases energy; energy must be input to break bonds.

Confusion between Heat and Temperature

Heat is energy transfer due to temperature difference; temperature is a measure of average kinetic energy.

Direction of Heat Flow (in Exothermic)

Heat flows out of the system, increasing the temperature of the surroundings.

Direction of Heat Flow (in Endothermic)

Heat flows into the system, decreasing the temperature of the surroundings.

Potential Energy Changes in Exothermic Reactions

The potential energy of the products is lower than that of the reactants.

Potential Energy Changes in Endothermic Reactions

The potential energy of the products is higher than that of the reactants.