CHEM EXAM IV

thermochemistry

study of heat absorbed or released during chemical and physical changes

energy

the capacity to supply heat or do work

work

a change in volume against a pressure

potential energy

energy an object has because of its relative position, composition, or condition

kinetic energy

energy an object has because of its motion

law of conservation of energy

during a chemical/physical change, energy is neither created nor destroyed, but it can change forms

thermal energy

random internal kinetic energy associated with the random motion of atoms and molecules internally in a system

temperature

quantitative measurement of particle speed

hot = high = fast moving particles

heat

the transfer of thermal energy between two bodies at different temperatures

heat flow

increases the thermal energy of one body and decreases the thermal energy of the other until both are the same

exothermic process

heat is released and/or absorbed by solution

ex. combustion reaction that uses a torch

endothermic process

heat is absorbed and/or provided by the solution

ex. cold pack

calorie

amount of energy required to raise one gram of water by 1*C

cal

Calorie / kilocalorie

quantifies food energy content

C

joule

the amount of energy used when a force of 1 newton moves an object 1 meter

J

James Prescott Joule

english physicist

joules are named for him

heat capacity

quantity of heat absorbed or released when a body of matter experiences a change in temperature change

extensive property

does a large pan or small pan have higher heat capacity

large pan

specific heat capacity

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

intensive property

calorimetry

measures the amount of heat transferred in or out of a substance

system

substance or substances undergoing the chemical or physical change

surroundings

all other matter that provide or absorb heat from a system

calorimeter

device that measures amount of heat involved in a chemical or physical processf

types of calorimeters

coffee-cup: two “cups” - can be industrial, not actual cups

bomb: used when the reaction releases gas

whole body: can hold a human being, used to compare heat under differing conditions

nutritional calorie

energy derived from metabolism of foods

thermochemistry

deals in the relationships between heat, work, and forms of energy

first law of thermodynamics

—>

expansion work

pressure-volume work

system pushes back the surroundings against a restraining pressure

surroundings compress a system

-q

-w

what type of reaction (endo/exothermic)

exothermic

state function

values that depend on the state of the substance, and not on how that state was reached

ex. internal energy, density

enthalpy

the sum of a system’s internal energy (U) and the mathematical product of its pressure (P) and volume (V)

most convenient choice for determining heat

enthalpy change

this is pressure-volume work

what does a thermochemical equation represent

changes in both matter and energy

what type of reaction does negative delta H represent? (endo/exothermic)

endothermic

standard state

a commonly accepted set of conditions used as a reference point for the determination of properties under other different conditions

The IUPAC standard state conditions:

Pressure of 1 bar (or 1 atm; 1 bar = 0.987 atm)

Solutions at 1 M concentration

standard enthalpy of combustion

enthalpy change when exactly 1 mole of a substance burns (combines vigorously with oxygen) under standard state conditions

heat of combustion

standard enthalpy of formation

enthalpy change for a reaction in which exactly 1 mole of a pure substance is formed from its constituent free elements in their most stable states under standard state conditions

Hess’s Law

If a process can be written as the sum of several stepwise processes, the enthalpy change of the total process equals the sum of the enthalpy changes of the various steps