Chem exam 3

Thermochemistry

the study of energy changes that occur during chemical reactions

chemistry is the study of

matter

? affects matter

energy

Energy

anything that has the capacity to do work

work

a force acting over a distance

Energy= work=

force x distance

heat

the flow of energy caused by a difference

Energy can be ? between objects through ?

exchanged

contact

Think of energy as a

quantity an object can possess

Think of heat and work as the 2 different ways that an

object can exchange energy with other objects

Kinetic energy

energy of motion/ energy that is being transferred

Potential energy

energy that is stored in an object or energy associated with the composition and position of the object

energy stored in the structure of a compound is

potential

internal energy (E)

the total energy contained within a system

Part of E is kinetic energy from ?

molecular energy

Thermal energy

translational motion, rotational motion, vibrational motion

part of kinetic energy

Part of E is ?

potential energy

Chemical energy

intermolecular and intramolecular forces of attraction and locations of atoms and bonds

type of potential energy

inter

one molecule and neighbor

intra

bond

electrical energy

kinetic energy associated with the flow of electrical charge

light or radiant energy

kinetic energy associated with energy transitions in an atom

heat or thermal energy

kinetic energy associated with molecular motion

Nuclear energy

potential energy in the nucleus of atoms

chemical energy

potential energy due to structure of atoms, attachment between atoms, atoms positions relative to one another or position in structure

The law of conservation of energy

energy cannot be crated nor destroyed only transferred

system

material or process within which we are studying the energy changes within

surroundings

everything else with which the system can exchange energy withou

when studying energy we are looking at the exchange of energy between the

system and surroundings

the amount of kinetic energy a. object has is directly proportional to its

mass and velocity

Joule (J)

amount one energy needed to move a 1 kg mass a distance of 2 meter

1J=

kg X m²/s²

Calorie (cal)

amount of energy needed to raise the temp of one gram of water 1 degree C

kcal=

energy needed to raise 1000 g of water 1 degree C food calories

what’s the difference between kcal and cal

kcal is the calories we consume and measure

kinetic energy formula

KE=1/2mv²

m=kg

v=m/s

First law of thermodynamics

the law of conservation of energy

Total amount of energy in universe is

constant

Conservation of energy requires that the

sum of the energy changes is system and surroundings must be zero

Change in energy of universe

0

change system + change surroundings

change in energy of system

-change surroundings

internal energy

sum of kinetic energy and potential energies of all the particles that compose the system

change in internal energy of a system only depends on the

amount of energy in system at the beginning and end

state function

mathematical function whose result only depends on the initial and final conditions not on process used/path taken

energy diagrams

a graphical way of showing the direction of energy flow during a process

if reactions have a lower initial energy than the products the change in energy will be

positive

if the reactants have a higher internal energy than the products the change in energy will be

negative

when energy flows out of system it must flow into the ?

change in internal energy system is ?

surroundings

negative

when energy flows into surroundings change in internal energy system is ?

positive

when energy flows into a system it must come from the ?

change in internal energy system is ?

surroundings

positive

when energy flows out of the surroundings change in internal energy system is ?

negative

How is energy exchanged?

between the system and surroundings through heat and work

q=

w=

heat(thermal) energy

work energy

There is no such thing as neg heat and work but the - sign tells us

what direction it is lost

q and w are not state functions because

their value depends on the process

positive heat (q)

system gains thermal energy

negative heat (q)

system loses thermal energy

positive work (w)

work done on system

negative work (w)

work done by system

change in internal energy positive (delta E)

energy flows into system

change in internal energy negative (delta E)

energy flows out of system

heat

exchange of thermal energy between the system and surroundings

Heat exchange occurs when

system and surroundings have a diff in temp

Temperature

the measure of amount of thermal energy within a sample of matter

Heat flows from matter with a high temp to matter with low temp until

objects reach the same temperature (thermal equilibrium)

when a system absorbs heat, it temp increases and is ? to amount of heat absorbed

directly proportional

Proportionality constant of heat is called? and units are in ?

heat capacity C

J/ degree C

J/K

q formula with specific heat

mass X C X (t final - t initial)

the heat capacity of an object depends on its

amount of matter and type of material

Specific heat capacity

amount of heat energy required to raise the temp of one gram of substance 1 degree C

used with pure elements and compounds

molar heat capacity

amount of heat energy required to raise the temp of one mole of a substance by 1 degree C

q hot =

-q cold

when 2 objects at different temps are placed in contact, heat flows from the material at higher temp to the material at lower temp until both materials

reach the same final temp

the amount of heat energy lost by the hot material=

the amount of heat gained by the cold material

PV work is caused by a

volume change against an internal pressure

when gases expand delta V is ? but the system is doing work on the surroundings so ? is negative

positive

W gas

As long as the external pressure is kept constant

w= -p X (V final - V initial)

We can determine change in internal energy by measuring

q + w

change in E= q system

How can we measure q system

we cannot observer the temp changes of individual chemicals involved in a reaction so instead we measure the temperature change in the surroundings

using insulated controlled surroundings

The surrounding area in a ? is usually made of a sealed insulated container with water

bomb calorimeter

q surroundings =? =?

q calorimeter

-q system

Bomb calorimeters are used to measure change in internal energy because

it is at a constant volume system

the heat capacity of the calorimeter is ?

amount of heat absorbed by calorimeter for each degree rise in temp and called calorimeter constant

enthalpy (H)

the sum of the internal energy of the system and the product of pressure and volume

H= and is a ?

E+PV

state function

Enthalpy change (dela H)

a reaction of heat evolved in a reaction at constant pressure

usually delta H and delta E are similar in value the difference is largest for reactions that

produce of use large quantities of gas

Exothermic reaction

heat is released by the system

endothermic reaction

heat is absorbed by the system

in an endothermic reaction the surroundings temperature ? due to absorption of some of its thermal energy by the reaction

drops

in an exdothermic reaction the surroundings temperature ? due to release of some of its thermal energy by the reaction

rises

The products of the reaction have ? in an endothermic reaction

more chemical potential energy than the reactants

The products of the reaction have ? in an exdothermic reaction

less chemical potential energy than the reactants

The system must ? heat in an endothermic reaction

absorb

The system must ? heat in an exothermic reaction

release

enthalpy change in a chemical reaction is an ? property

extensive

the more reactants (moles) you have the ? the enthalpy change

larger

reactions done in aqueous solutions are at constant pressure and measured using

constant pressure calorimetry

Hess’s law

the change in enthalpy for a stepwise process is the sum of the enthalpy changes of the steps

Standard state

the state of material at a defined set of conditions