Chem 130 exam 3: Ch. 9.1-4

Energy

capacity to do work

Work

result of a force acting through a distance

Heat

flow of energy caused by a temperature difference

Kinetic energy

energy associated with motion

Thermal energy

energy associated with the temperature of an object

Potential energy (IMFS and bonds)

energy associated with position or composition of an object

Chemical energy

the energy associated with relative positions of electrons and nuclei

Thermodynamics

study of energy and its interconversions

1st Law of Thermodynamics

the total energy of the universe is constant

2nd Law of Thermodynamics

the entropy (disorder) of the universe increases over time

3rd Law of Thermodynamics

a perfect crystal at zero kelvin has zero entropy (not possible)

Internal energy

the sum of kinetic and potential energy of all the particles in a system

Symbol for internal energy

U/E

A change/reaction that releases heat

exothermic process

A change/reaction that absorbs heat

endothermic process

The SI unit of heat, work, and energy is the

joule (J)

A joule (J) is defined as:

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

Symbol for heat capacity

C

Symbol for heat (energy transferred due to temperature difference)

q

Heat capacity is determined by both the _____ and _____ of substance that absorbs or releases heat.

type, amount

Heat is an ______ property (its value is proportionate to its amount)

extensive

Intensive property of a substance that represents the quantity of heat required to raise the temperature of 1 gram of the substance by 1 degree Celsius (or 1 kelvin)

specific heat capacity/c

Symbol for specific heat capacity

c

If we know the mass of a substance and its specific heat, we can determine the:

amount of heat, q, entering or leaving the substance

Symbol for temp. change (Tfinal - Tinitial)

ΔT

If a substance gains thermal energy, ΔT has a _____ value.

positive

If a substance loses thermal energy, ΔT has a _____ value.

negative

q = (_______ heat) x (______ of substance) x (________ change)

specific, mass, temperature

Equation for determining the amount of heat (q) entering/leaving a substance

q = c x m x Δ𝑇

Thermal energy transfer relationship

qsystem = -qsurroundings (opposite sign)

The substance or substances undergoing the chemical or physical change

system

All other matter, including components of the measurement apparatus, that serve to either provide heat to the system or absorb heat from the system

surroundings

A device used to measure the amount of heat involved in a chemical or physical process.

calorimeter

The qa = -qb relationship shows that:

the heat gained by substance a is equal to the heat lost by substance b

qenergy + qsurroundings =

0

Calorimetry problems with two substances (finding final temperature)

When two substances exchange heat and the final temperature is unknown, set the heat equations equal so total heat change equals zero. This is because heat lost by the hot substance equals heat gained by the cold substance (energy is conserved).

Measures heat released from combustion reactions at constant volume by tracking temperature change in surrounding water

bomb calorimeter

Bomb calorimeter equation

q = -Ccal Δ𝑇

Calorimiter heat capacity (Ccal) equation:

Ccal = (m water x C water) + Cbomb

Normal calorimeter problem answer units are usually ___, but bomb calorimeter answers are usually in ___.

J, kJ

The heat of the reaction is the ______ of the heat absorbed by the calorimeter:

negative, qrxn = -qcal

In bomb calorimeter problems, ΔErxn​ is = to _____.

qrxn = -qcal

q =

qrxn

In bomb calorimeter problems, ΔErxn =

-Ccal x ΔT

In regular calorimetry problems, qrxn =

-qsolution

For bomb calorimeter problems, if they want ΔE_rxn in kJ/mol, you must

divide the heat of the reaction by the moles of the substance burned.

metal final temp =

water final temp

Enthalpy is often referred to as the “____ of the reaction”

heat

Symbol for heat released/absorbed in a reaction

ΔH

Heat flows into the reaction = ____thermic, heat flows out of the reaction = ____thermic

endo, exo

H represents the

total heat in a system

Energy is transferred into a system when it absorbs heat (_) from the surroundings or when the surroundings do work (_) on the system.

q, w

(___ q is heat flow in; ___ q is heat flow out)

positive, negative

The work, w, is positive if it is done ___ the system and negative if it is done ___ the system.

on, by

work done as a system expands or contracts against external pressure

expansion (pressure-volume) work

The relationship between internal energy, heat, and work can be represented as:

ΔU = q + w

Property depending only on the state of a system, and not the path taken to reach that state (mountain analogy)

state function

Enthalpy is a ____ function

state

Enthalpy change equals heat of reaction at constant pressure.

Δ𝐻 = qp

-Δ𝐻 = _____, Δ𝐻 = ______

exothermic reaction, endothermic reaction

When a problem says heat produced or released

Assign q as negative immediately and use that value in calculations (do not flip the sign at the end).

Set of physical conditions as accepted as common reference conditions for reporting thermodynamic properties; 1 bar of pressure, and solutions at 1 molar concentrations, usually at a temperature of 298.15 K

standard state

If temp ____, q is _______. If temp _______, q is ______.

increases, positive, decreases, negative

If the problem involves an aqueous solution, you usually assume the density is:

1.00 g/mL

If the problem involves an aqueous solution, you usually assume the mass is:

volume (mL) = mass (g)

If the problem involves an aqueous solution, you usually assume the specific heat is:

4.184

When a problem involves aqueous solutions (like HCl(aq), NaOH(aq), salt solutions, etc.), you usually assume the solution behaves like water unless told otherwise. Therefore, the mass should be the ________ and the specific heat should be _______.

total ml of reactants, 4.184

If the question asks for amount of heat, whether it says absorbed or produced, the answer should always be ________ because it’s just talking about how much there was.

positive

If the question asks for thermodynamic heat, ex. q, qrxn, ΔH, enthalpy change, heat of reaction, these answers need signs that are determined by whether the reaction is _______ or _________.

endo/exothermic

There are 3 relationships betwene chemical equations and ΔHrxn: 1) _______ by cofactor, _____ changes if equation is reversed, and ______’s Law.

multiply, sign, hess

If a chemical equation is multiplied by some factor, the ΔHrxn is also ______ by _________.

multiplied, the same factor

If a chemical equation is reversed the ΔHrxn ________.

changes sign

_________ states that if a chemical reaction can be expressed as the sum of a series of steps, then the ΔHrxn for the overall equation is the sum of the heats of reaction for each step.

Hess’s Law

ΔH =

kJ/mol

Standard enthalpy of formation (Δ𝐻°f)

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

Short Hess’s Law definition: The change in enthalpy for a stepwise process is the ____ of the enthalpy changes of the steps.

sum

Combustion means a substance reacts with oxygen to form _____ and ____.

CO2, H2O

______ must always be included in the reactants of a combustion reaction.

oxygen

The standard enthalpy change for a reaction is equal to the sum of _______ - sum of ________.

products, reactants

lattice energy (ΔH_lattice)

energy required to separate one mole of an ionic solid into its component gaseous ions

Enthalpy change (ΔH) using bond energies formula is the sum of the energy required to ______ all bonds in the reactants (energy “in”, positive sign) plus the energy released when all bonds are _____ in the products (energy “out,” negative sign).

break, form

The standard enthalpy change for the endothermic reaction that breaks all the bonds in the molecule is equivalent to the _____________.

sum of all bond energies in the molecule

Bond energy

The energy required to break a specific covalent bond in one mole of gaseous molecules

Breaking bonds =

negative (endothermic)

Forming bonds =

positive (exothermic)

Heat of combustion =

negative answer

Specific heat capacity/c formula

c = q/m x Δt

Water boils at

100 degrees c