chem final concepts

effective collisions between reactants

collision where the total/average kinetic energy of the molecules colliding is greater than the activation energy of the elementary step

catalyst

must change the rate of slow step (changes delta H of individual steps, not overall rxn)

energy

the potential to cause change or the work that a force did to cause change

law of conservation of energy (1st law of thermodynamics)

energy cannot be created nor destroyed but it can change in form or type

kinetic energy

energy of movement

potential energy

stored energy; energy available that can cause change

what happens to potential energy when bonds are broken?

potential energy of atoms bonded increases

what happens to potential energy when bonds are formed?

potential energy of atoms bonded decreases

why does something feel hot or cold?

high kinetic energy → hot

low kinetic energy → cold

what causes something to change from cooler to warmer?

1) change in potential energy → change in kinetic energy of molecules around the rxn

2) transfer of KE from one object to another

internal energy

KE + PE

how can changes in E be expressed?

heat (q) or work (w)

Change in E of system

q of system + w of system

heat capacity (C)

energy in J needed to change an object by 1 degree C (mixture/multiple components)

specific heat (Cs)

energy in J required to change 1 g by 1 degree C (pure substance)

w= -P * change in V

w=work, P=atmospheric pressure, V= change in volume caused by change in composition (reactants to products)

when the volume of the particles present in the products is larger than the reactants, the reaction will do work on the surroundings, and the reaction _ energy in the form of work

loses

when the volume of the particles present in the reaction decreases, the reaction will have work done on it by the surroundings, and the reaction _ energy in the form of work

gains

q=n* delta H

used in a constant pressure condition (coffee cup calorimeter)

q=n* delta E

used in a constant volume condition (bomb calorimeter)

for a bomb calorimeter, what is the change of volume for a rxn that occurs?

0

for a bomb calorimeter, what is the value of work for a rxn that occurs?

0

when a rxn happens in a bomb calorimeter, how can internal energy be expressed?

heat only

in a coffee cup calorimeter, what can the change of volume for the reaction that occurs be?

positive or negative

in a coffee cup calorimeter, what is the value of work for the reaction that occurs?

positive, negative, or zero

when a rxn happens in a coffee cup calorimeter, how can internal energy be expressed?

in the form of both work and heat

2 methods of finding limiting reactant

1) compare amounts of reactants

2) if both reactants fully react, which one forms a smaller amount of product?

endothermic reaction

heat is absorbed by the reaction, and the bonds present in the products are weaker (higher PE) than the bonds present in the reactants

formation reaction

a specific type of rxn where 1 mole of the compound of interest is produced from pure elements of the compound in their naturally occurring states (ex/ o2 (g), c (s) or h2 (g)). the change in enthalpy is called the enthalpy of formation

exothermic reaction

heat is released by the reaction, and the bonds present in the products are stronger (lower PE) than the bonds present in the reactants

entropy (s)

thermodynamic value that quantifies energy distribution within a system

positive delta s

favorable to reaction spntaneity

spontaneous process

process/reaction that occurs naturally without any continual external force (E); rate or speed of rxn doesn’t contribute to if the rxn is spontaneous or not

how does temperature affect entropy?

high temp → high KE → higher entropy

how does the total # of particles affect entropy?

higher # of particles →higher entropy

how does the physical state of the reactants or products affect entropy?

s of solid < s of liquid < < < s of gas; s of aqueous ion/solute ~ s of liquid

gibbs free energy (delta g = delta h - (temp in kelvin * delta s))

delta h and delta s affect this, contributing to whether a rxn is spontaneous or not

delta g is negative

reaction is spontaneous (free energy is released)

negative delta h

favorable to spontaneity

either both positive or both negative delta h and delta s

temperature-dependent spontaneity

intermolecular forces

attractions between molecules

intramolecular forces

attractions within molecules (bonds)

bonds are shorter

atoms more attracted to each other

larger electronegativity

more polar

miscible

if strongest imf present between the two molecules matches, then two molecules are miscible