Thermochemistry - Honors Chem

Thermochemistry

the study of the transfers of energy as heat that accompany chemical reactions and physical changes in matter, focusing on concepts like enthalpy, entropy, and calorimetry.

Thermochemistry for Exo and Endothermic

Exothermic Reactions produce heat since there is less Potential Energy stored in bonds for the products compared to the reactants. The opposite is true for Endothermic Reactions. In exothermic reactions, energy is released to the surroundings, while in endothermic reactions, energy is absorbed from the surroundings.

Difference between heat and temperature

Heat - energy that transfers between matter due to temperature differences.

Temperature - a measure of average Kinetic Energy of the particles.

Different units of energy

Joule - a unit of energy that is defined as the amount of work done by a force of one Newton acting through one meter.

Newton is a unit of force that gives a mass of one kilogram an acceleration of one meter per second per second.

calorie - a unit of energy that is defined as the amount of heat energy required to raise the temperature of 1g of water by 1o Celsius.

Kilocalorie - a unit of energy that is defined as the amount of heat energy required to raise the temperature of 1L of water by 1o Celsius. 1kcal = 1Cal = 1000cal

Energy Flow/Heat Transfer

warm objects will always transfer heat to cooler objects. This flow of energy continues until thermal equilibrium is reached, where both objects are at the same temperature.

Conduction

the process by which heat or electricity is directly transmitted through a substance when there is a difference of temperature or of electrical potential between adjoining regions, without movement of the material.This occurs primarily in solids, where particles are in close contact and can transfer kinetic energy through collisions.

Convection

the movement caused within a fluid (liquid or gas) by the tendency of hotter (and therefore less dense) material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat.

Radiation

the emission of energy as electromagnetic waves or as moving subatomic particles, especially high-energy particles.

Specific Heat Capacity

the amount of energy required to raise the temperature of 1g of a substance by 1oC.

if a Specific Heat Capacity for a substance is low, it heats up _____ ; if a Specific Heat Capacity for a substance is high, it heats up _____

quickly, slowly

Specific Heat Capacity Formula

Q = m c ΔT

Calorimeter

an instrument that is used to determine the heat capacity of an object using a physical or chemical process.

entropy

a measure of disorder (or chaos) a system has; quantifies the amount of energy for atoms/molecules as they become more spread out.It indicates the spontaneity of processes.

Entropy is generally ____ in gasses and lower in solids

higher because they possess more energy and are spontaneously moving around a given space

enthalpy

the sum of a thermodynamic system’s internal energy and the product of its pressure and volume

Second Law of Thermodynamics

Entropy of an isolated system will always increase over time and can never be negative. The universe tends to lead to disorder.

If ΔH is negative

reaction is exothermic

If ΔH is positive

reaction is endothermic

Bond Energy

the measure of strength (in kJ/mol) which determines the amount of energy needed to break a chemical bond between two atoms.

difference between heat of fusion and heat of vaporization

heat of fus is for solid and liquid

heat of vap is for gas and liquid

Heat of Fusion

the quantity of energy needed to melt or freeze a substance under a constant pressure

Heat of Vaporization

the quantity of energy needed to evaporate or condense a substance under a constant pressure

Latent Heat

energy used to loosen the bonds between separate molecules and overcome the intermolecular forces

Molar Heat of Fusion

the amount of heat absorbed by one mole of a substance as it transitions from a solid to liquid (or amount released to transition from liquid to solid)

Molar Heat of Vaporization

the amount of heat absorbed by one mole of a substance as it transitions from a liquid to gas (or amount released to transition from gas to liquid)

Hess’s Law

the overall enthalpy change in a reaction is equal to the sum of enthalpy changes for the individual steps in the process

First Law of Thermodynamics

energy in a closed system remains constant and will not change; therefore, energy can’t be created nor destroyed, but only transformed from one thing to another

similar to law of conservation of mass