apchem ch.5: thermochem

thermochemistry

the study of heat flow in a chemical process

KMT (kenetic molecular theory)

the average KE of a substance is directly proportional to absolute temperature (kelvin)

heat

the sum of all kinetic energy in a system

system

part of universe under study

surroundings

anything not in the system

exothermic

heat is leaving the system into the surrounding (-)

endothermic

heat is entering the system from the surrounding (+)

internal energy

the sum of all kinetic and potential energy in a system

kinetic energy

Energy of motion (KE=1/2mv^2)

potential energy

energy of position, change depending on how particles change

internal energy is not heat

can not talk about it like endo/exothermic

change in internal energy

ΔE = Efinal - Einitial
Ef and Ei not known exactly but can know the difference

state function

a value that is dependent only on the conditions at which a system exists and not how it got there

ΔE < 0

internal energy of system decreased

ΔE > 0

internal energy of system increased

ΔE = q + w

q = heat
w = work = -PΔV (pressure/volume)

+w

surrounding is doing work on system

-w

system is doing work on surrounding

q

heat transfered under any condition

+q

heat into the system

-q

heat out of the system

enthalpy

heat transferred at constant pressure

gas to liquid

heat released, exothermic, negative

will 4.0g of CH4 release more or less than 802kJ?

less since 4.0g of CH4 is less than one mole of it

what stores the energy?

bonds (energy create energy by forming bonds)

calorimetry

the measurement of heat flow

law of conservation of energy

energy can neither be created nor destroyed

heat capacity

the heat amount needed to change the temperature by 1°C

specific heat

the amount of heat required to raise the temperature of 1g of substance by 1°C or 1K

hess's law

a reaction can be described by a series of thermochemical equations

standard enthalpy of formation

the heat transferred when exactly 1 mole of product (a single product) is formed from its elements in their standard state

ΔHrxn (ΔHfº)

Σ(n • ΔHfº products) - Σ(n • ΔHfº reactants)

bond enthalpy

the energy required to break a covalent bond in the gaseous state (always positive)

more electrons in the bond?

more energy needed to break the bond

bonds ΔHrxn

bonds broken (reactant bonds) - bonds formed (product bonds)

structural formula

shows connectivity between bonds

molecular formula

only shows number and type of atoms