Unit 9 - Thermochemistry

Question 1

Thermochemistry

Answer 1

The study of energy changes during a chemical reaction or change of state (solid, liquid, gas).

Question 2

Chemical Potential Energy

Answer 2

The energy stored in chemical bonds. (Lines with no Slope on the Heating Curve)

Question 3

Heat

Answer 3

Energy that transfers from one object to another due to a difference in temperature between them. Heat always flows from the warmer to the cooler object.

Question 5

Melting

Answer 5

Make or become liquefied by heat. (Solid to Liquid)

Question 6

Freezing

Answer 6

Freezing or solidification is a phase transition in which a liquid turns into a solid when its temperature is lowered below its freezing point. (Liquid to Solid)

Question 7

Condensation (Precipitation)

Answer 7

The conversion of a vapor or gas to a liquid.

Question 8

Vaporization (Evaporation)

Answer 8

The conversion of a liquid into a gas.

Question 9

Heat of Fusion

Answer 9

The energy required to change a gram of a substance from the solid to the liquid state without changing its temperature.

Question 10

Solidification

Answer 10

Freezing or solidification is a phase transition in which a liquid turns into a solid when its temperature is lowered below its freezing point. (Liquid to Solid)

Question 11

Heat

Answer 11

A form of energy that flows between two samples of matter because of their differences in temperature.

Question 12

Temperature

Answer 12

A measure of the intensity of heat, i.e. the hotness or coldness of a sample. or object.

Question 13

Kinetic Energy

Answer 13

In Thermochemistry, the energy an object possesses due to its change in temperature is called kinetic energy. (Sloped lines on the Heating Curve)

Question 14

Potential Energy

Answer 14

Potential energy is that energy which an object has because of its position. It is called potential energy because it has the potential to be converted into other forms of energy, such as kinetic energy. (Lines with no Slope on the Heating Curve

Question 15

Endothermic

Answer 15

Reaction in which the system absorbs energy from its surroundings in the form of heat.

Question 16

Exothermic

Answer 16

An exothermic reaction is a chemical reaction that releases energy in the form of light or heat.

Question 17

Activation Energy

Answer 17

The minimum energy required to start a chemical reaction

Question 18

Collision Theory

Answer 18

Molecules have to collide in a certain way with a certain amount of activation energy in order to form a new product.

Question 20

Heating Curve

Answer 20

A plot of the temperature versus time.

Question 21

How to speed up the Rate of a Reaction

Answer 21

1. Shrink the container or increase concentration. 2. Increase the number of particles. 3. Speed up the particles by adding heat. 4. Break up clumps into individual particles. 5. Use a catalyst.

Question 22

Catalyst

Answer 22

A substance that causes a chemical reaction to happen more quickly.

Question 25

Solid

Answer 25

Solid is one of the four fundamental states of matter. It is characterized by structural rigidity and resistance to changes of shape or volume.

Question 26

Liquid

Answer 26

Liquid is one of the four fundamental states of matter, and is the only state with a definite volume but no fixed shape. A liquid is made up of tiny vibrating particles of matter, such as atoms, held together by intermolecular bonds.

Question 27

Phase Changes

Answer 27

Question 28

Gas

Answer 28

One of four main states of matter, composed of molecules in constant random motion. Unlike a solid, a gas has no fixed shape and will take on the shape of the space available. Unlike a liquid, the intermolecular forces are very small; it has no fixed volume and will expand to fill the space available.

Question 29

Boiling

Answer 29

Boiling is the rapid vaporization of a liquid, which occurs when a liquid is heated to its boiling point.

Question 30

Boiling Point

Answer 30

The temperature at which the vapor pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding environmental pressure. At the boiling point the gas and liquid phase exist in equilibrium.

Question 31

Evaporation versus Boiling

Answer 31

Question 32

Melting Point

Answer 32

The melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. At the melting point the solid and liquid phase exist in equilibrium.

Question 34

Law of Conservation of Energy

Answer 34

Energy can not be created nor destroyed during a chemical reaction

Question 35

Heat Capacity

Answer 35

Heat capacity is the amount of heat energy required to change the temperature of a substance

Question 36

Endo or Exothermic?

Answer 36

Exothermic reaction graph

Question 38

Phase Diagram most substances (e.g. CO2)

Answer 38

slight positive slope; more dens in (l) phase;
triple point: s, l, g in equilib.
critical point: T and P above which there is no distinction between l and g

Question 39

Phase Diagram H2O

Answer 39

negative slope bc H2O has lower density in (s) than (l); increase in P favors more dense version.

Question 40

Which phase changes are endothermic? Which are Exothermic? Is bond breaking Endothermic or Exothermic?

Answer 40

Question 41

Phase Diagram Questions

Answer 41

Question 42

Heating Curve Questions

Answer 42

Question 43

thermochemical equation

Answer 43

thermochemical equation

• balanced chemical equations with heat changes taken into account
• think of it as (and treat it as) a reactant or a product

Question 44

Enthalpy (H)

Answer 44

-the heat content of a system (or chemical reaction)

Question 45

CaO (s) + H₂O (l) → Ca(OH)₂(s) + 65.2 kJ
Change in H = - 65.2 kJ
Endo or Exo?

Answer 45

Exo
heat is a product and change in H is negative

Question 46

2 NaHCO₃ (s) + 129 kJ → Na₂O (s) + H₂O (g) + CO₂(g)
Change in H = +129 kJ
Endo or Exo ? How to tell?

Answer 46

Endo
heat is a reactant and change in H is positive

Question 48

five ways to tell if a reaction is exothermic

Answer 48

graph slopes down
heat is given off (to the surroundings)
change in H is negative
temperature of “surroundings” increases
heat is written as a product

Question 49

five ways tell if a reaction is endothermic

Answer 49

graph slopes up
heat is absorbed (from the surroundings)
change in H is positive
temperature of “surroundings” decreases
heat is written as a reactant