3.1.4 energetics

Question 1

is bond breaking an exothermic or endothermic process?

Answer 1

Endothermic

Question 2

is bond making an exothermic or endothermic process?

Answer 2

exothermic

Question 3

What is the enthalpy change?

Answer 3

The heat energy change at constant pressure

Question 4

What is the symbol for enthalpy change?

Answer 4

Delta H

Question 5

what are the units of enthalpy change?

Answer 5

KJmol-1

Question 6

what are the standard values of temperature and pressure?

Answer 6

Temperature: 298K (25°C)

Pressure: 100kPa

Question 7

what is the standard enthalpy change at a temperature of 298K and a pressure of 100kPa?

Answer 7

Delta H 298

Question 8

when is the reaction said to be exothermic?

Answer 8

If more energy is released when new bonds are formed

than was needed to break the bonds in the reactants

Then the difference in energy is released to the surroundings, and the reaction said to be exothermic

Question 9

As energy is lost by the system to the surroundings, the sign of enthalpy change of the system is what?

Answer 9

negative

Question 10

What does the energy level diagram for an exothermic reaction look like?

Answer 10

Question 11

when is a reaction said to be endothermic?

Answer 11

If more energy is needed to break the bonds in the reactants

than was released when new bonds are formed

Then the difference in energy is absorbed from the surroundings

and the reaction is said to be endothermic

Question 12

as energy is gained by the system from the surroundings, the sign of the enthalpy change of the system is what?

Answer 12

positive

Question 13

what does the energy level diagram for an endothermic reaction look like?

Answer 13

Question 14

do strong bonds need more or less energy to break?

Answer 14

More

Question 15

definition: bond enthalpy

Answer 15

The enthalpy change when a covalent bond is broken, so the values are always positive

Question 16

definition: mean bond enthalpy

Answer 16

The average enthalpy change when a specific bond is broken in a range of compounds

Question 17

what I mean bond enthalpies used to calculate?

Answer 17

The enthalpy change

Question 18

Definition: bond dissociation energy

Answer 18

The energy needed to break a particular covalent bond

Question 19

definition: standard enthalpy change of formation

Answer 19

The enthalpy change when one mole of a compound is formed from its elements with all reactants and products in their standard states and under standard conditions

Question 20

definition: standard enthalpy change of combustion

Answer 20

The enthalpy change when one mole of a substance is completely burned in excess oxygen with all reactants and products in their standard states and under standard conditions

Combustion reactions are always exothermic

Question 21

definition: standard enthalpy change of reaction

Answer 21

The enthalpy change when a reaction occurs in the molar quantity shown in the chemical equation, under standard conditions, with all reactants and products and their standard states

Question 22

The standard enthalpy of formation of an element must be what?

Answer 22

zero

Question 23

can the same reaction represent more than one type of reaction?

Answer 23

Yes

Question 24

what’s Hesses law also known as?

Answer 24

The first law of thermodynamics

Question 25

what does the first law of thermodynamics state?

Answer 25

Energy cannot be made or destroyed, but it can be converted from one form to another

Question 26

what does Hesses law state?

Answer 26

The total enthalpy change for a reaction is independent of the route taken

Question 27

A=

Answer 27

C-B

Question 28

extra info

Answer 28

Question 29

What is the equation for enthalpy change?

Answer 29

q=mc delta T

Question 30

Hey, what's the number for specific heat capacity?

Answer 30

4.18

Question 31

How does a simple colorimeter work?

Answer 31

- a spirit burner containing a liquid fuel is weighed - The spirit burner is placed beneath a copper can (colorimeter) containing a known volume of water (at a known temperature) and then lit - The water is stirred at regular intervals - When the temperature of the water has risen by at least 10°C, the flame is put out on the spirit burner is reweighed - Using the massive fuel used and the temperature rise of the water, the amount of heat energy released per gram of fuel can be calculated

Question 32

is a bomb colorimeter or a simple calorimeter more accurate, why?

Answer 32

A bomb calorimeter is more accurate this is because the heat loss to the surroundings is reduced to 0

Question 33

What is calorimetry use to find?

Answer 33

The enthalpy changes for a reaction taking place in the solution

Question 34

in an exothermic reaction, heat is .............. on the temperature of the water in the solution ..............

Answer 34

Released Increases

Question 35

in an endothermic reaction, the heat energy ............. comes from the water in the solution, and the temperature of the solution ...............

Answer 35

Absorbed Decreases

Question 36

how do you make this experiment more accurate?

Answer 36

- Using a polystyrene cup and a beaker provides some insulation and placing a lid on top of the cup reduces heat loss