thermochem

thermochemistry

study of energy changes that occur during chemical reactions and changes in state

chemical potential energy

energy stored in the chemical bonds of a substance

energy changes occur as

either heat transfer or work, or a combination of both.

heat

q- energy that transfers from one object to another because of a temperature difference between the objects

system

part of universe you focus your attention on

surroundings

everything else in the universe

law of conservation of energy

during any chemical or physical process, the energy of the universe remains unchanged.

endothermic process

heat is absorbed from the surroundings. the system gains heat as the surroundings lose heat

exothermic process

releases heat to its surroundings. the system loses heat as the surroundings gain heat.

heat flow is measured with what

calories and joules

calorie

quantity of heat needed to raise the temperature of 1g of pure water 1 degree celsius

one dietary Calorie (calorie in food) equals

1 kilocalorie = 1000 calories

1 joule

0.239 cal

heat capacity

the amount of heat needed to increase the temperature of an object exactly 1 degrees celsius

the heat capacity of an object depends on

both its mass and chemical composition

specific heat

amount of heat it takes to raise the temperature of 1 g of substance 1 degrees celsius. represented by C

C (the specific heat) =

q/(m x delta T) = heat (j or cal)/(mass(g) x change in temperature in celsius)

q

heat

m

mass

delta T

final temperature - initial temperature

calorimetry

measurement of heat flow in or out of a system for chemical and physical processes

enthalpy

total heat of a system

delta H is determined by

measuring the heat flow of the reaction at constant pressure

q=

delta H

q surr=

m x c x delta T

q sys=

-m x c x delta T

the sign of delta H is positive for

endothermic reactions

the sign of delta H is negative for

exothermic reactions

in a chemical reaction, the enthalpy change for the reaction can be written as either a

reactant or product

thermochemical reaction

chemical equation that includes the enthalpy change

heat of reaction

enthalpy change for the chemical equation. usually seen as delta H

molar heat of fusion

the heat absorbed by one mole of a solid substance as it melts to a liquid at a constant temperature

molar heat of solidification

heat lost when one mole of a liquid substance solidifies at a constant temperature.

the quantity of heat absorbed by melting is

exactly the same as the quantity of heat released when the liquid solidifies. delta Hfus = -delta H solid

molar heat of vaporization

the amount of heat required to vaporize one mole of a given liquid at a constant temperature

molar heat of condensation

amount of heat released when one mole of vapor condenses at its normal boiling point

the quantity of heat absorbed by a vaporizing liquid is

exactly the same as the quantity of heat released when the vapor condenses- delta Hvap= -delta H cond