Thermochemistry

Question 0

Define thermal energy

Answer 0

Thermal energy is energy associated with the random motion of atoms and molecules.

Question 1

Define radiant energy

Answer 1

Energy that comes from the sun and is earth’s primary energy source.

Question 2

Define chemical energy

Answer 2

Chemical energy is energy stored within the bonds of chemical substances.

Question 3

Define nuclear energy

Answer 3

Nuclear energy is the energy stored within the collection of neutrons and protons in the atom.

Question 4

Define potential energy

Answer 4

Potential energy is the energy available by virtue of an objects position.

Question 5

Define heat

Answer 5

Heat is the transfer of thermal energy between two bodies that are at different temperatures.

Question 6

What is temperature?

Answer 6

Temperature is a measure of thermal energy. Thermal energy is not the same as temperature.

Question 7

Define thermochemistry

Answer 7

Thermochemistry is the study of heat change in chemical reactions.

Question 8

What is the system?

Answer 8

The system is the specific part of the universe that is of interest in the study.

Question 9

Difference between open, closed, and isolated?

Answer 9

Open allows for the exchange of mass and energy, closed only allows for the exchange of energy, and isolate allows no exchanges.

Question 10

Define exothermic process.

Answer 10

An exothermic process is any process that gives off heat (transfers thermal energy from the system to the surroundings).

Question 11

Define endothermic process

Answer 11

An endothermic process is any process in which heat has to be supplied to the system from the surroundings.

Question 12

Define thermodynamics

Answer 12

Thermodynamics is the scientific study of the interconversion of heat and other kinds of energy.

Question 13

What are state functions?

Answer 13

State functions are properties that are determined by the state of the system regardless of how that condition was achieved. Energy(u), pressure(p), volume(v), and temperature(t).

Question 14

What is enthalpy?

Answer 14

Enthalpy is a measure of the total energy of a thermodynamic system, including the system’s internal energy as well as its volume and pressure. It is represented by H; however, it cannot be measured directly and the change of enthalpy is measured instead. So ΔH is what is used in calculations usually.

Question 15

The first law of thermodynamics is…

Answer 15

Energy can be converted from one form to another, but cannot be created or destroyed.

Question 16

What does ΔU = q + w mean?

Answer 16

ΔU is the change in internal energy of a system. q is the heat exchange between the system and the surroundings w is the work done on (or by) the system. w = -PΔV

Question 17

What is enthalpy (H) used for?

Answer 17

Enthalpy is used to quantify the heat flow into or out of a system in a process that occurs at constant pressure.

ΔH = H (products) - H (reactants).

ΔH = heat given off or absorbed during a reaction at

(This is for constant pressure processes)

Question 18

Describe some basic rules of thermochemical equations.

Answer 18

The stoichiometric coefficients always refer to the number of moles of a substance.

If you reverse a reaction, the sign of ΔH changes.

If you multiply both side of the equation by a factor n, then ΔH must change by the same factor n.

The physical states of all reactants and products must be specified in thermochemical equations, because the state does effect the ΔH. For example:

H₂O_(s) H₂O_(I) ΔH = 6.01 kJ/mol

H₂O_(I) H₂O_(g) ΔH = 44.0 kJ/mol

Question 19

How is ΔU calculated in general for a constant-pressure process?

Answer 19

ΔU = q + w

= q_p - PΔV

Where:

the subscripted “_p” denotes constant-pressure condition

Question 20

Define specific heat

Answer 20

The specific heat of a substance is the amount of heat (q) required to raise the temperature of one gram of the substance by one degree Celsius.

Specific heat is designated by C.

Question 21

What is the formula to calculate how much heat has been absorbed?

Answer 21

q = mcΔT

Where:

q is heat energy

m is mass

c is heat capacity heat of the substance

ΔT is final temperature - initial temperature in Celsius

(specific heat is sometimes written as s)

Question 22

What is the formula for calculating work?

Answer 22

w = -PΔV

Where:

w is work

P is pressure

ΔV is the final volume - initial volume

Question 23

Define heat capacity

Answer 23

Heat capacity is the amount of heat required to raise the temperature of a given quantity of the substance by one degree Celsius