Thermochemistry

Question 1

What is chemical potential energy?

Answer 1

Potential energy stored in the bonds holding atoms together. The amount of energy depends on the type of bond and how they’re bonded.

Question 2

What is heat?

Answer 2

Energy transferred from one object to another due to a temperature difference between them. Represented by ( q )

Question 3

What is the Law of Conservation of Energy?

Answer 3

Energy cannot be created or destroyed. It can only be transformed or dispersed. Heat lost be one object = heat gained by another object.

Question 4

What is the system?

Answer 4

The aspect of the universe which we are focused on

Question 5

What are the surroundings?

Answer 5

Everything else in close proximity to the system

Question 6

What does endothermic mean?

Answer 6

A change in which energy is absorbed from the surroundings to the system. This increases the potential energy of the system. The system will feel colder than the surroundings until the temperature of the system and the surroundings are equal.

Question 7

What does exothermic mean?

Answer 7

A change in which energy is released from the system into the surroundings. Increases the potential energy of the surroundings. The system will feel warmer than the surroundings until the temperature of the system and surroundings are equal.

Question 8

What direction does heat flow from?

Answer 8

Warmer to cooler

Question 9

What is heat capacity?

Answer 9

The amount of energy required to raise the temperature of an object by 1 degree Celsius.

Question 10

What is specific heat capacity?

Answer 10

The amount of energy required to raise the temperature of one gram of an object by 1 degree Celsius.

Question 11

What do each letter in q=mct(delta t) represent?

Answer 11

q = amount of heat (Joules). delta t = change in temperature (degrees Celsius). c = specific heat capacity (Joules per gram degree Celsius). m = mass in grams.

Question 12

What does a positive and negative q value signal about the reaction?

Answer 12

Positive q = endothermic
Negative q = exothermic

Question 13

What is q = vc(delta t) used for?

Answer 13

Water. V = volume.

Question 14

What are the different units for specific heat capacity?

Answer 14

Joules per gram degree Celsius.
Kilojoules per kilograms degree Celsius.
Kilojoules per liters degree Celsius.
Joules per milliliter degree Celsius.

Question 15

What is enthalpy?

Answer 15

The total amount of energy associated with a substance or reaction. Change in enthalpy measured as (delta H) in joules.

Question 16

What are the ways to express enthalpy?

Answer 16

As real numbers. Ex: Delta H = -65.2 KJ
As a potential energy diagram.
As a thermochemical equation. Ex: CaO(s) + H20(l) –> Ca(OH)2(s) + 62.5 KJ

Question 17

What are the x and y axis of a potential energy diagram?

Answer 17

X is potential energy and Y is reaction.

Question 18

What is molar enthalpy?

Answer 18

The enthalpy per mole of a substance (H), measured in KJ/J per mole

Question 19

What do the letters in Delta H = nH mean?

Answer 19

Delta H is enthalpy change.
n is moles
H is molar enthalpy.

Question 20

What is a phase change?

Answer 20

Change in state. Potential energy stored in the bonds of a substance during a phase change. Phase changes take place at melting and boiling points.

Question 21

What is Heat of fusion?

Answer 21

Enthalpy change of a substance going from solid to liquid

Question 22

What is heat of solidification?

Answer 22

Enthalpy change of substance going from liquid to solid.

Question 23

What is the relationship between Hfus and Hsol?

Answer 23

DeltaHfus = -DeltaHsol

Question 24

What is heat of vaporization?

Answer 24

Enthalpy change of a substance going from liquid to gas.

Question 25

What is the heat of condensation?

Answer 25

Enthalpy change of a substance going from gas to liquid.

Question 26

What is the relationship between Delta Hvap and Delta Hcon

Answer 26

Delta Hvap = -Delta Hcon

Question 27

What is calorimetery?

Answer 27

The precise measure of heat flow in or out of a system for chemical or physical processes.

Question 28

What are calorimeters?

Answer 28

Apparatus used to measure heat flow in or out of a system. The system being the substances undergoing chemical change and the surroundings being the water.

Question 29

What is the relationship between the system and surroundings in a calorimetry expirement?

Answer 29

qsurroundings = -qsystem. nH = -(mcdeltat)

Question 30

How is heat flow calculated?

Answer 30

Using q = mcdeltat or q = vcdeltat

Question 31

Does a phase change involve change in temperature?

Answer 31

No

Question 32

What does a temperature change represent on a heating or cooling curve?

Answer 32

A change in kinetic energy

Question 33

What does a phase change represent on a heating or cooling curve?

Answer 33

A change in potential energy

Question 34

What is the slope of a heating curve?

Answer 34

Positive

Question 35

What is the slope of a cooling curve

Answer 35

Negative

Question 36

What is Hess’s Law?

Answer 36

If you add two or more thermochemical equations to give a final equation, then you can also add the heats of reaction to give the final heat of reaction

Question 37

How is Hess Law (long) used?

Answer 37

Manipulate the equations you are given to result in one target equation. Adjust the enthalpy changes of the given equations as needed as they are manipulated. At the end, add the deltaH values together for a final enthalpy change.

Question 38

How is Hess’s Law (short) used?

Answer 38

Delta H of reaction = (Sum moles times enthalpies of formation for the products) - (Sum of moles times enthalpies of formation for the reactants).

Question 39

What may be needed for multi step equations?

Answer 39

Hess’s law short, deltaH = nH, and n = m/M