Thermochemistry

Enthalpy change

________ depends on the physical states of reactants and products and these states must be specified.

Delta H

________ can be determined experimentally by measuring heat flow for a reaction at constant pressure.

If delta V is + →

expansion of gas; system does work on surroundings and w is negative.

internal energy

Like ________ E, both P and V are state functions.

Surroundings

________: everything outside of the system.

PV work

________ "is work involved in expansion or compression of gases.

sign of delta H

Reversing the direction of a reaction changes the ________.

enthalpy change

If the coefficients of a chemical reaction are multiplied by some factor, the ________ must also be multiplied by that factor.

delta H

If ________ is positive, the reaction is endothermic.

Internal energy

________, U, of a system: the sum of ALL potential and kinetic energies of the components of the system.

delta H

If ________ is negative, the reaction is exothermic.

System

part of the universe that we are studying

Surroundings

everything outside of the system

Open system

matter & energy exchange with surroundings

Closed system

exchanges energy as work and/or heat (but not matter)

Isolated system

neither matter nor energy exchanged

First law of thermodynamics

energy is conserved

Internal energy, U, of a system

the sum of ALL potential and kinetic energies of the components of the system

delta U = Ufinal

Uinitial

At constant pressure

w = -P(delta V)

If delta V is

→ compression of gas; work is done on the system and w is positive

At constant pressure

delta H = delta E + P(delta V)

Heat capacity

the amount of heat required to raise the temperature of an object by one degree C or K

Specific heat

the heat capacity of one gram of a substance; Cs

Enthalpy of formation

the enthalpy change for the reaction in which one mole of a substance is made from its constituent elements in their elemental (most stable) forms

Standard enthalpies of formation

measured under standard conditions