Energy in Chemical Reactions - Chemistry B Unit 2 ✨

bond energy

the energy that is required to break chemical bonds

chemical bond

the force that holds atoms, molecules, or ions together to form chemical compounds

endothermic reaction

a chemical reaction that absorbs energy from its surroundings

enthalpy (H)

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

exothermic reaction

a chemical reaction that releases energy into the environment

law of conservation of energy

energy can be neither created nor destroyed, only transformed between forms

ΔH (enthalpy change)

the change in enthalpy of products minus reactants; negative for exothermic, positive for endothermic

Hess’s law

the total enthalpy change is the same whether a reaction occurs in one step or multiple steps

standard enthalpy of formation

the enthalpy change when one mole of a compound forms from its elements in their standard states

bond dissociation enthalpy

the energy required to homolytically cleave a bond, yielding radicals

system

the reactants and products in a chemical reaction being studied

surroundings

everything outside of the system being studied

open system

a system that can exchange both energy and matter with its surroundings

closed system

a system that can exchange energy but not matter with its surroundings

isolated system

a system that cannot exchange energy or matter with its surroundings

state function

a property that depends only on the state of the system, not on how it was reached

spontaneous process

a process that occurs without outside intervention and has negative Gibbs free energy

Gibbs free energy (G)

the energy associated with a chemical reaction that can be used to do work; G

calorimeter

an apparatus used to measure heat flow between the system and the surroundings

activation energy

the minimum energy required to initiate a chemical reaction by breaking bonds of the reactants

transition state

a high-energy, unstable arrangement of atoms at the peak of the activation energy barrier

collision theory

the theory that molecules must collide with proper orientation and sufficient energy to react

reaction coordinate diagram

a graph of potential energy versus reaction progress showing activation energy and enthalpy change

catalyst

a substance that speeds up a reaction by providing an alternative pathway with lower activation energy without being consumed

electronegativity

a measure of an atom’s ability to attract electrons in a chemical bond

chemical reaction system

the reactants and products in a particular reaction being studied

covalent bond

a chemical bond formed by the sharing of electron pairs between atoms

ionic bond

a chemical bond formed by the electrostatic attraction between oppositely charged ions

polar covalent bond

a covalent bond in which electrons are shared unequally due to differences in electronegativity

Lewis structure

a diagram showing the arrangement of electrons in a molecule using dots and lines

resonance

the delocalization of electrons across adjacent atoms in a molecule to lower overall energy

conduction

the transfer of energy by direct contact between substances

convection

the transfer of energy by movement of fluid currents

radiation

the transfer of energy as electromagnetic waves without needing a medium

specific heat capacity (c)

the energy required to raise the temperature of 1 gram of a substance by 1 °C

q

m·c·ΔT

calorimetry

the experimental measurement of heat flow in physical and chemical processes

heat capacity

the amount of heat needed to raise the temperature of an object by 1 °C; equal to mass times specific heat capacity

adiabatic process

a process in which no heat is exchanged between the system and its surroundings

kinetic energy (KE)

the energy of motion of a particle or object

potential energy (PE)

the stored energy of a particle or system based on its position or composition

thermochemistry

the branch of chemistry that studies the energy changes accompanying chemical and physical processes

Maxwell–Boltzmann distribution

a statistical distribution of molecular kinetic energies at a given temperature

degrees of freedom

the independent ways in which a molecule can store energy, including translational, rotational, and vibrational motion

internal energy (U)

the total energy contained within a system, including kinetic and potential energies of particles

enthalpy vs. internal energy

under constant pressure, enthalpy change equals internal energy change plus pressure–volume work (ΔH

heat vs. work

two forms of energy transfer; heat is due to temperature difference, work is due to force acting over a distance

relative potential energy

the difference in potential energy between reactants and products that determines the net energy change of a reaction

lattice energy

the energy released when gaseous ions combine to form an ionic solid

Born–Haber cycle

a thermochemical cycle used to calculate lattice energy based on Hess’s law

bond order

the number of shared electron pairs between two atoms in a bond; higher bond order indicates stronger bonds

Madelung constant

a factor that quantifies the geometric contribution to lattice energy in ionic crystals

thermodynamic stability

the tendency of a substance to remain in its current state; more stable substances have lower potential energy and negative formation enthalpies