Ch. 6 - Thermochemistry

thermochemistry

the study of heat and energy in chemical rxs

energy

the capacity to do work or transfer heat

mechanical energy

energy an object possesses due to its position and/or motion

• total energy of a system, the sum of both potential energy and kinetic energy

kinetic energy (KE)

the energy of motion

potential energy

the energy of an object that is related to its position (energy of height)

system

a specified portion of the universe that is studied

• ex: hot metal, chemical rxn

surroundings

the part of the universe that is separate from a system of study

• ex: the apparatus, the container, everything else

open system

both matter and energy can move between the system and the surroundings

• ex: fireplace burning wood; heat and gaseous products escape into the atmosphere, while cooler air enters the fireplace

closed system

emery but not matter can move between the system and the surroundings

• ex: pressure cooker; heat escapes the system but water and steam is trapped inside

isolated system

neither matter nor energy can leave or enter the system

• ex: calorimeter: prevents transfer of heat and energy between system and surroundings

work (w)

the energy resulting from a force acting on an object over a distance

• ex: a person pushing a stalled car down a road work on the car

heat (q)

the flow of energy that causes a temperature change in an object or it’s surroundings

• ex: an ice cube melting in a person’s hand

law of conservation of energy

energy cannot be created or destroyed, just transferred from one form to another

• no net gain or loss of energy

first law of thermodynamics

the energy of the universe is constant

internal energy (U)

the sum of all kinetic and potential energies of a system

internal energy (U) formula

delta U = q + w

q

system gains/loses heat

w

work is done one/done by the system

delta U

the system gains/loses internal energy

signs (+ or -)

• (+) - indicates energy enters a system

• (-) - indicates energy leaves a system

state function

a function that is independent of the path taken to achieve its value

• ex: internal energy (delta U)

path function

a function that is dependent on the sequence of steps that live the system from its initial state to its final state

• ex: work and heat - their values depend on the path taken

• depends on the sequence of steps between initial and final states

pressure-volume work

the work done on or by a system when there is volume change against an external pressure

pressure-volume work forumula

w = -P delta V

enthalpy (delta H)

the um of internal energy of a system and the product of its pressure and volume change

energy required to run the rxn

• total heat of a system

• state function which means its value depends only on the current state of the system

• can be absorbed or released

• H = U + PV

enthalpy (delta H) formula

• delta H = q sub p

• H = U + PV

endothermic process

a process in which heat is absorbed from outside the system; delta H is positive

• ex: instant cold packs, melting ice

exothermic process

a process in which heat is transferred from the system to the surroundings; delta H is negative

• ex: packets of hand warmers, wood burning in fireplace

specific heat ( c )

the quantity of heat required to raise the temperature of 1g of a substance by 1C

heat formula

q = mc delta T

• q - heat, J

• m - mass, g

• c - specific heat J/g deg C

• delta T - change in temperature, deg C

calorimetery

a lab technique for quantifying heat transfer between substances by measuring the temperature changes of the substances involved