Topic 5: Energetics

Question 1

How do you convert celsius to kelvin?

Answer 1

Celsius+273= K

Question 2

What is the definition of heat?

Answer 2

measure of the total kinetic energy of particles in a substance

Question 3

What is the definition of temperature?

Answer 3

Measure of average kinetic energy of particles in a substance

Question 4

Heat energy flows from___to___

Answer 4

High temp. object to low temp. obj.

Question 5

The Kelvin scale is based on…Therefore, zero kelvin refers to…

Answer 5

Kinetic energy. 0K= no movement

Question 6

Enthalpy can be calculated using this equation:

Answer 6

q=mc (delta)T. m= mass (mass of water unless specified), c= specific heat capacity (usually for water), Delta T= change in temp

Question 7

What is specific heat capacity?

Answer 7

Energy required to raise the temp. of 1 g of substance by 1K

Question 8

What is the specific heat capacity of water?

Answer 8

4.186 J/ (gC)

Question 9

For q=mc(delta)T, how can you tell if the reaction is endo or exothermic?

Answer 9

if q is positive, endothermic, temp increased. If q is negative, exothermic, temp. decreased

Question 10

What is enthalpy (H)?

Answer 10

The amount of heat energy stored in a substance within its chemical bonds.

Question 11

What is an exothermic reaction? What does its enthalpy graph look like?

Answer 11

More energy is released than absorbed. Therefore, reactants have more energy than products, so reactants are higher on the enthalpy graph. Products are more stable.

Question 12

Does an exothermic rxn have a positive or negative delta H (change in enthalpy)?

Answer 12

Negative. energy released is negative

Question 13

What is an endothermic rxn? What does its enthalpy graph look like?

Answer 13

More energy is absorbed than released. Therefore, products are higher on the graph than reactants. Reactants are more stable.

Question 14

What is standard enthalpy change?

Answer 14

Enthalpy change (delta H) of a reaction w/ standard conditions and standard states of the substances. Measured in kJ/mol.

Question 15

What are the values for STP?

Answer 15

289 K, 101.3 kPa, 1 mol/L

Question 16

What is standard enthalpy change of formation?

Answer 16

energy change when 1mol of compound is formed from its elements in standard states and conditions

Question 17

How do you calculate standard enthalpy change of formation?

Answer 17

The sum of the delta H of products minus the sum of delta H of reactants.

Question 18

What is the standard enthalpy change of formation for an element?

Answer 18

zero

Question 19

How do you take the q=mc delta T equation and use it to find enthalpy change?

Answer 19

divide the q value by the number of moles

Question 20

What is the standard enthalpy of neutralization?

Answer 20

enthalpy change when a strong acid and base react to form 1 mol H2O. Always exothermic.

Question 21

What are five steps to calculate standard enthalpy of neutralization?

Answer 21

1) find # moles of acid/base
2) Find limiting reactant and # moles of H2O that can be produced
3) Add volumes of acid and base together, assuming that 1 cm^3 = 1 g, to get the mass
4) Use that mass for q=mcdeltaT
5) Use q/n

Question 22

What is Hess’ law?

Answer 22

Regardless of the multiple steps of a rxn, the change in enthalpy is the sum of all the enthalpy changes. Therefore, you can manipulate reaction equations to find the change in enthalpy for the whole rxn.

Question 23

What is calorimetry?

Answer 23

process of measuring amount of heat released/absorbed during a reaction. Change in heat can be measured by observing the temp of the H2O or surroundings.

Question 24

How can calorimetry be performed?

Answer 24

bomb shell, cup/lid/thermometer/ flame combustion, etc.

Question 25

What are 5 assumptions that can lead to errors in calorimetry?

Answer 25

all heat is transfered to H2O, All solution is dissolved, mass of H2O is constant, there is unlimited O2, there are standard conditions

Question 26

What is average bond enthalpy?

Answer 26

energy required to break 1 mol of the same type of bond averaged across many similar compounds

Question 27

Is bonds forming endo/exo?

Answer 27

Bonds forming=exothermic. Releases energy

Question 28

Is bonds breaking endo/exo?

Answer 28

Bonds breaking=endo. Takes energy to break bonds

Question 29

How do you use avg. bond enthalpy to calculate enthalpy change?

Answer 29

Sum of energy of bonds broken minus sum of energy of bonds formed. Formation is negative, but you don’t subtract a negative; just subtract the absolute value of formation.

Question 30

What are two forms of oxygen in the atmosphere?

Answer 30

O2 and O3, ozone

Question 31

What does ozone do?

Answer 31

It absorbs UV radiation

Question 32

Why are O3 bonds easier to break than O2 bonds?

Answer 32

Double bond in O2 is stronger

Question 33

What equation can you use to calculate the wavelengths required to break O3 bonds?

Answer 33

(h x c)/ wavelength = Photon energy

Question 34

What wavelength breaks O2 bonds?

Answer 34

UV radiation w/ wavelength less than 242 nm

Question 35

What wavelength breaks O3 bonds?

Answer 35

UV radiation w/ wavelengths less than 330 nm

Question 36

What is the ozone-oxygen cycle?

Answer 36

Process by which O3 is continually regenerated in the stratosphere

Question 37

What are the steps of the ozone-oxygen cycle?

Answer 37

High energy UV radiation breaks O2, O3 forms. Lower energy UV breaks O3. Significant because dangerous UV has been absorbed, so the stratosphere is warmer