Unit 10: Thermochemistry

Question 1

Thermochemistry

Answer 1

Study of energy changes that occur during chemical reactions and changes in state

Question 2

Chemical potential energy

Answer 2

Energy stored in the chemical bonds of a substance

Question 3

Heat always flows from…

Answer 3

A warmer object to a cooler object

Question 4

When studying energy changes, system is…

Answer 4

A part of a universe on which you focus your attention

Question 5

Surroundings

Answer 5

Everything else in the universe

Question 6

Law of conservation of energy

Answer 6

Any chemical or physical process, energy is neither created nor destroyed

Question 7

Endothermic process

Answer 7

Absorbs heat from surroundings
–> System gains heat as surroundings cool down
— Example: man getting warm from fire camp

Question 8

Exothermic process

Answer 8

Releases heat into surroundings
–> System looses heat as surroundings heats up
— Example: a woman runing and sweating

Question 9

Heat flow is measured in two common units

Answer 9

Calorie and joule
1 Calorie = 1kilocalorie = 1000 calories

Question 10

Heat capacity of an object

Answer 10

The amount of heat needed to increase the temperature of an object exactlt is 1C
–> The heat capacity of an object depends on both it’s mass and chemical compositions

Question 11

Specific heat of a substance

Answer 11

Amount of heat it takes to raise the temperature of 1g of the substance 1C

Question 12

How to calculate specific heat (c) of a substance

Answer 12

c = q/m△t = heat(joules or calories)/mass(g)change in temperature (C)

Question 13

Calorimetry

Answer 13

Precise measurment of the heat flow into or out of a system for chemical and physical process
–> In calorimetry, the heat released by the system is equal to the heat absorbed by its surroundings. Conversively, the heat absorbed by a system is equal to the heat released by its surroundings

Question 14

Calorimeter

Answer 14

The insulated device used to measure the absorption or release of heat in chemical or physical process

Question 15

Enthalpy (H)

Answer 15

The heat content of a system at constant pressure is the same as a property

Question 16

In a chemical equation…

Answer 16

The enthalpy change for the reaction can be written as either a reactant or a product

Question 17

Thermochemical equation

Answer 17

A chemical equation that includes the enthalpy change

Question 18

Heat of reaction

Answer 18

Enthalpy change for the chemical equation exactly as it is written

Question 19

Molar heat of fusion △Hfus

Answer 19

The heat absorbed by one mole of a solid substance as it melts to a liquid at a constant temperature

Question 20

Molar heat of solidification △Hsolid

Answer 20

Heat lost when one mole of a liquid solidifies at a constant temperature

Question 21

The quantity of heat absorbed by a melting solid is…

Answer 21

Exactly the same as the quanitity of heat released when the iquid solidifies; that is, △Hfus = -△Hsolid

Question 22

Molar heat of vaporization (△Hvap)

Answer 22

The amount of heat necessary to vaporize one mole of given liquid

Question 23

Molar heat of condensation (△Hcond)

Answer 23

The amount of heat released when 1mol of vapor condenses at the normal boiling point

Question 24

The quantity of heat absorbed by a vaporizing liquid is…

Answer 24

Exactly the same as the quantity of heat released when the vapor condenses that is △Hvap = -△Hcond

Question 25

Molar heat of solution (△H soln)

Answer 25

The enthalpy change caused by dissolution of one mole of substance
–> During the formarion of a solution, heat is either released or absorbed

Question 26

Hess’s law of heat summation

Answer 26

States that if you add two or more thermochemical equations to give a final heat of reaction
–> Hess’s law allows you to determine the heart of reaction indirectly

Question 27

Standard heat of formation (△Hf^o) of a compound

Answer 27

Change in enthalpy that accompanies the formation of one mole of a compound from its elements with all substances in their standard states at 25C
–> For a reaction that occurs at standard conditions, you can calculate the heat of reaction by using standard heat of formation
△H = △Hf(products) - △Hf(reactants)