Grade 12 AP Chemistry - Thermochemistry Terms + Initial Formulas

Energy

the capacity to do work or transfer heat

Work

the E used to cause an object to move against a force

Heat

E transfer from a hot object to a cold one

Kinetic E

the E of motion

Kinetic E Formula**************

E_k = ½mv²

where E_k = kinetic E in J

m = mass in kg

v = velocity in m/s

Kinetic E increases as the speed of the object or its mass ________

increases

Potential E

stored E

Thermochemistry

study of the relationships between chemical rxns and E changes that involve heat

Joule (J)

SI unit for E

1 J = 1kg-m²/s²

Calorie (cal)

another unit for E

amount of E required to raise the temp of 1g of water by 1 degree C

Conversion between cal and J

1 cal = 4.184 J

Conversions between cal, Cal and kcal

1 Cal = 1000 cal = 1 kcal

System

portion of the universe that is being studied for E changes

Surroundings

everything else that is not the system

Open vs Closed vs Isolated System

open: matter and E can be exchanged with the surroundings

closed: matter cannot be exchanged with the surroundings, but E can

isolated: neither matter or E can be exchanged with the surroundings

Force

any push or pull exerted on an object

Work formula (with F and d)*************

w = F x d

where w = work in J

F = force in kg-m/s²

d = distance in m

First Law of Thermodynamics

E cannot be created or destroyed

Internal E

sum of all kinetic + potential E in the system (+rotational, translational and vibrational movement of atoms)

Change in internal E formula (not with q and w)

ΔE = E_final - E_initial

where ΔE = change in internal E

E_final = final internal E of the system

E_initial = initial internal E of the system

a +ve value of ΔE means the system has ______ E from its surroundings

gained

a -ve value of ΔE means the system has ____ E to its surroundings

lost

Any increase in the E of the system results in a ________ in the E of the surroundings.

decrease

Change in internal E formula (with q and w)

ΔE = q + w

where ΔE = change in internal E

q = heat in J

w = work in J

q sign conventions

+ve = system gains heat

-ve = system loses heat

w sign conventions

+ve = work done on system

-ve = work done by system

ΔE sign conventions

+ve = net gain of E by system

-ve = net loss of E by system

Endothermic

system absorbs heat

Exothermic

system loses heat

State Function

property of a system in which we only care about the before and after (and not how it got to the after)

e.g. internal E

The value of a state function depends ONLY on the PRESENT state of the system, not the ____ the system took to reach that state.

path

Chemical vs Physical vs Nuclear Change

chemical: new substance created

physical: change in state/shape

nuclear: change in the nucleus

Fission vs Fusion

fission: splitting a larger atom into 2 or more smaller ones

fusion: joining 2 or more small atoms into a larger one

Is fission or fusion more typically used today in nuclear power plants? Why is the other one not used?

fission is used

fusion is not used because it requires large amounts of E to sustain the high temp required for fusion

Pressure-Volume Work

work involved in the expansion or compression of gases

-ΔH represents

an exothermic change

+ΔH represents

an endothermic change

Thermochemical Equation

E value is included as a term in the chemical equation

Endothermic rxns ___________ heat, therefore the enthalpy term is written on the _______ side.

absorb/require, reactant

Exothermic rxns ______ heat, therefore the enthalpy term is written on the _______ side.

release, product

Potential E Diagram

graph where you put the reactants and products and indicate E levels

‘rxn progress’ goes on x-axis and ‘potential E, E_p (kJ)’ goes on y-axis

The magnitude of ΔH is __________ to the amount of reactant.

proportional

The forward rxn is equal in _________ but _________ in sign to reverse rxn’s ΔH.

magnitude, opposite

ΔH varies with _____ of a substance…therefore you must specify it in chemical rxns.

state

Calorimetry

measurement of heat flow

Calorimetre

measures heat flow

Heat Capacity (C)

amount of heat required to raise the temp of an object by 1 degree C

Specific Heat Capacity (c)

amount of heat required to raise the temp of 1g of an object by 1 degree C

Molar Heat Capacity (C_m)

heat capacity of one mol of a substance

formula regarding ΔT, c, q and m

q = mcΔT

where q = heat E in J

m = mass in g

c = specific heat capacity in J/g degrees C

ΔT = change in temp

Specific heat capacity of water

4.184 J/g degrees C

Δ in Enthalpy (ΔH)

difference between E absorbed and E released when breaking/forming chemical bonds in rxns

Thermal E

measure of the kinetic E of the particles in a system

Heat

E transfer from hot to cold object

Temperature

measure of the average kinetic E of the particles in a system

ΔH formula regarding P, ΔV, ΔE***********************

ΔH = ΔE + PΔV

where ΔH = change in enthalpy (in ???)

ΔE = change in internal E (in J)

P = pressure (in ???)

ΔV = change in volume (in ???)

Work formula (with P and ΔV)*************************

w = -PΔV

where w = work (in J)

P = pressure (in ???)

ΔV = change in volume (in ???)

What are the units for heat capacity, C?

J/°C

What are the units for specific heat capacity, c?

J/g°C

What are the units for molar heat capacity, C_m?

J/mol°C

Formula for ΔH_total, n and ΔH

ΔH_total = nΔH

Formula with ΔH_system and q_surroundings

ΔH_system = ±|q_surroundings|