Thermochemistry

Question 1

Thermochemistry:

Answer 1

The study of heat changes associated with physical, chemical and nuclear processes.

Question 2

Potential Energy:

Answer 2

Stored energy.

Question 3

Kinetic Energy:

Answer 3

The energy of motion.

Question 4

Exothermic Processes:

Answer 4

Energy is released to its surroundings. It is mathematically negative.

Question 5

Endothermic Processes:

Answer 5

Energy is absorbed from its surroundings. It is mathematically positive.

Question 6

If energy is a reactant it is ___________.

Answer 6

endothermic

Question 7

If energy is a product it is __________.

Answer 7

exothermic

Question 8

Photosynthesis is (endo/exo)thermic.

Answer 8

endo

Question 9

Cellular respiration is (endo/exo)thermic

Answer 9

exo

Question 10

What is total enthalpy affected by?

Answer 10

Molecular structure of the substance and the mass of the substance

Question 11

What are the units for enthalpy?

Answer 11

kJ

Question 12

What are the units for molar enthalpy?

Answer 12

kJ/mol

Question 13

Describe the endothermic chemical reaction.

Answer 13

Bonds of the reactants are broken and energy is required.

Question 14

Describe the exothermic chemical reaction.

Answer 14

Bonds of the products are reformed and energy is released.

Question 15

Does an exothermic visual diagram start high or low?

Answer 15

High.

Question 16

Does an endothermic visual diagram start high or low?

Answer 16

Low.

Question 17

What is the bump in a reaction diagram?

Answer 17

Activation energy.

Question 18

What is necessary for a reaction diagram?

Answer 18

Title, labelled axis’, enthalpy change, reactants and products, units.

Question 19

What three things affect kinetic energy?

Answer 19

Temperature, amount, and type of substance.

Question 20

How do you calculate Ek?

Answer 20

mc(change in)t

Question 21

How do you calculate molar enthalpy?

Answer 21

Ep/n

Question 22

What are the units for specific heat capacity?

Answer 22

J/gC

Question 23

Specific heat capacity:

Answer 23

The amount of heat energy needed to raise the temperature of 1 g of a substance 1C/1K

Question 24

Which has a higher heat capacity, metal or rubber?

Answer 24

Rubber

Question 25

When Ek is negative, a substance is _______ ____.

Answer 25

cooling down

Question 26

When Ek is positive, a substance is _______ ____.

Answer 26

heating up

Question 27

How do you do calorimetry with a styrofoam calorimeter?

Answer 27

Calculate Ek, multiply by -1 to get Ep, Ep/n

Question 28

What has a 1:1 ratio with 1g?

Answer 28

1 mL

Question 29

How do you do calorimetry with a metal can calorimeter?

Answer 29

Ek = mct(water) + mct(can), * -1 = Ep, Ep/n

Question 30

When in a combustion reaction is water a liquid?

Answer 30

In a bomb calorimeter or a living system ie. human urine

Question 31

When in a combustion reaction is water gas?

Answer 31

In an open environment ie. boiling a pot of water

Question 32

What are the Molar Enthalpy of Formation values derived from?

Answer 32

Bomb calorimeter data.

Question 33

Commonly, molar enthalpy of formation reactions are (end/ex)othermic.

Answer 33

end

Question 34

How do you find the molar enthalpy of a decomposition?

Answer 34

Flip the sign from the data booklet.

Question 35

What is the molar enthalpy of formation for elements assumed to be?

Answer 35

Zero.

Question 36

When Ep is released in formation, what is the result?

Answer 36

A more thermally stable compound.

Question 37

Which is more thermally stable and why? SO3(l) H = -441.0 kJ SO3(g) H = -395.7 kJ

Answer 37

The liquid one because more Ep was released.

Question 38

Catalysts:

Answer 38

Can be used to speed up reactions that are exothermic but react slowly. They reduce the activation energy required to move the reaction forward. (They provide an alternate reaction path.)

Question 39

When a catalyst is added, does the Molar Enthalpy of Formation/Decomposition value change?

Answer 39

No.

Question 40

Which compound is more thermally stable, glucose or sucrose?

Answer 40

Sucrose.

Question 41

Basic rules to apply to Hess's law:

Answer 41

1. Balanced equation with molar enthalpy 2. Decompose one mole of each reactant and change the enthalpy sign. Multiply enthalpy by coefficients 3. Form the correct number of moles for the products and multiply by coefficients 4. Ignore elements as they will typically sort themselves out 5. Add the equations, and they should add up to the original equation.

Question 42

How do you use Hess's Law Shortcut?

Answer 42

1. Write a balanced equation for which H is needed for one mol 2. Add all the H values of the compounds on the products side 3. Add all the H values on the reactant side 4. Multiply H values by coefficients if needed 5. Subtract the sum of the reactants from the sum of the products