Chapter 9 Enthalpy

Question 1

what is enthalpy

Answer 1

measure of heat energy in a chemical

Question 2

what is the symbol for enthalpy

Answer 2

H

Question 3

what is enthalpy change

Answer 3

the difference in enthalpies between the products and reactants

Question 4

what is the enthalpy change formula

Answer 4

ΔH = H(products) - H(reactants)

Question 5

what is conservation of energy

Answer 5

fundemental law of science that states that energy cannot be created or destroyed

Question 6

what is EXOTHERMIC

Answer 6

transfer of energy from the system to the surroundings

Question 7

what is ENDOTHERMIC

Answer 7

transfer of energy from the surroundings to the system

Question 8

what does an enthalpy profile diagram show

Answer 8

the relative enthalpies of the reactants and products and the enthalpy change

Question 9

how does the enthalpy diagram show if a reaction is endothermic or exothermic

Answer 9

exothermic reactions have a negative enthalpy change

endothermic reactions have a positive enthalpy change

Question 10

what is activation energy

Answer 10

the minimum amount of energy that must be supplied to the system before the reaction can take place

Question 11

define standard conditions

Answer 11

conditions under which most experiments are and most closely resemble typical working conditions of temperature and pressure

Question 12

how are standard physical conditions represented

Answer 12

⦵ in the superscript

Question 13

what is the standard pressure value

Answer 13

100kPa

Question 14

what is the standard temperature value

Answer 14

298K

25C

Question 15

what is the standard concentration value

Answer 15

1moldm^-3

Question 16

what is the standard state

Answer 16

the normal physical state of a substance under standard temperature and pressure

Question 17

what is the standard enthalpy change of reaction

Answer 17

the enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions

Question 18

what is the symbol for standard enthalpy change of reaction

Answer 18

ΔrH⦵

Question 19

what is the standard enthalpy change of formation

Answer 19

the enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions

Question 20

what is the symbol for standard enthalpy change of formation

Answer 20

ΔfH⦵

Question 21

what is standard enthalpy change of combustion

Answer 21

the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions

Question 22

what is the symbol for standard enthalpy change of combustion

Answer 22

ΔcH⦵

Question 23

what is standard enthalpy change of neutralisation

Answer 23

energy change that accompanies the reaction of an acid by a base to form one mole of H2O(l) under standard conditions

Question 24

what is the symbol for standard enthalpy change of neutralisation

Answer 24

ΔneutH⦵

Question 25

what three quantities are required to work out energy change

Answer 25

mass specific heat capacity temperature change

Question 26

how is mass calculated

Answer 26

it is the mass of the water in the aqueous solutions so you take the volume and times it by the density; 1g/cm

Question 27

what is the specific heat capacity value

Answer 27

4.18

Question 28

what is the heat energy equation

Answer 28

``` q = m x c x ΔT energy = mass x specific heat capacity x temperature change ```

Question 29

what are the three steps to calculate ΔcH

Answer 29

>calculate the energy change >calculate the amount in moles of substance burned >do q/n to find ΔcH

Question 30

what are the four reasons why ΔcH may be different from the theoretical or expected

Answer 30

>heat loss to surroundings >incomplete combustion >evaporation of substance >non-standard conditions

Question 31

what are the three steps to calculate ΔrH

Answer 31

>calculate the energy change , q >calculate the amount of moles of the reactant that is not in excess >do q/n to find ΔrH

Question 32

what are the three steps to calculate ΔneutH

Answer 32

>calculate the energy change , q >calculate the amount in moles of the base + acid that was reacted >do q/n to find ΔneutH

Question 33

what is average bond enthalpy

Answer 33

the energy required to break one mole of a specified type of bond in a gaseous molecule

Question 34

why does average bond enthalpy have limitations

Answer 34

the actual bond enthalpy can vary depending upon the chemical environment of the bond

Question 35

which energy is endothermic and which is exothermic

Answer 35

energy required to break bonds is endothermic | energy released when bonds break is exothermic

Question 36

what is the enthalpy change of reaction equation

Answer 36

ΔrH = Σ(bond enthalpies in products) - Σ(bond enthalpies in reactants)

Question 37

what is Hess' Law

Answer 37

the total enthalpy change for an indirect route is the same as that for the direct route

Question 38

what is the value for all ΔneutH⦵ reactions

Answer 38

-57kJmol^-1