Units 5-7

Question 1

A coal burning power plant generates electrical power at a rate of 500 MW (1 MW = 5.00 x 10^6 J/s). The plant has an efficiency of 37.5% for the conversion of heat to electricity. Calculate the electrical energy in Joules generated in one year of operation and the heat energy used for that purpose

Answer 1

1.58 x 10^16 J electrical energy generated
4.20 x 10^16 J heat energy used

Question 2

A single serving bag of potato chips has 70 Cal (70 kcal) of chemical potential energy.
Assuming that all of this energy goes toward keeping your heart beating, how long (how many days) can these chips sustain a heartbeat of 80 beats per minute? (1 kcal = 4.184 kJ, and each heartbeat requires approximately 1 J of energy)

Answer 2

2.93 x 10^5 J –> 2.54 days

Question 3

Write the balanced equation that describes the combustion of hydrogen

Answer 3

2 H2 (g) + O2(g) –> 2 H2O (g)

Question 4

What is an exothermic v endothermic reaction?

Answer 4

Exothermic will release energy; endothermic will absorb energy

Question 5

What are advantages and disadvantages for using hydrogen as a fuel to produce energy?

Answer 5

advantage: large amount of energy per gram, H2O product of consumption is safe
disadvantages: explosive gas, not readily avaliable and requires a lot of energy input

Question 6

What are the top 3 energy producers

Answer 6

China, USA, Russia

Question 7

How do you solve for energy change?

Answer 7

(energy of bonds broken) - (energy of bonds formed)
ex: 3196 kJ - 3239 kJ = -43 kJ, energy released exothermic

Question 8

What are the difference between cellulose and starch for creating ethanol?

Answer 8

Starch: digestible by humans; polymer through a-link units
Cellulose: - non-digestible for humans; polymer by b-linked units

Question 9

When pentane burns in oxygen it releases 58 kJ/g. Is there more energy with the reactant or products? What would the overall energy change be, postive or negative?

Answer 9

More energy in the reactants than the products; the energy change would be -58kJ/g

Question 10

The amount of energy released when pentane burns in oxygen is 58 kJ/g. Boiling 1L of water requires approximately 330kJ of heat. Assuming that your pentane heater is 90% efficient (you can use 90% of the total heat produced by the combustion of pentane for your heating process), how many grams of propane would you need to boil 1L of water?

Answer 10

6.3 g pentane burned
( (kJ / g ) –> kJ needed to grams)

Question 11

if 2.7 moles of Na reacts in this equation, how many moles of oxygen are consumed? How many moles of product are formed? (hint molar ratio)
4 Na (s) + O2 (g) —> 2Na2O (s)

Answer 11

0.68 mol O2 consumed
1.4 mol Na2O (product) are formed

Question 12

What is the balanced equation for the combustion of octane?

Answer 12

2 C8H18 (l) + 25 O2 (g) ⎯→ 16 CO2 (g) + 18 H2O (g or l)

Question 13

What mass of water (in kg) is released into the atmosphere from the combustion of 1 tank full
of gas? (assume 1 tank of gas is 15 gallons and 1 gallon is 2.48kg)

Answer 13

60.6 kg

Question 14

How many times more CO2 was present billions of years ago compared to today? (if 400 ppm today)

Answer 14

1250 times more CO2 billions of years ago

Question 15

Although the US produces more per capita, China produces the most CO2 per country,
estimated to be 10,291,927 tons. How much of this mass is just carbon (not CO2 just C )

Answer 15

2.808 x 10^6 tons

Question 16

What causes greeenhouse effect?

Answer 16

Atoms in the atmosphere absorbing infrared radition causing them to spin; human causes is trapping more heat than a normal functioning greenhouse effect

Question 17

How many moles of methane are in 1.3 grams of methane?

Answer 17

0.081 mol CH4

Question 18

What gases contribute to anthropogenic climate change

Answer 18

CO2 and CH4

Question 19

What is the formula for magnesium hydroxide?
What is the molar mass of this compound

Answer 19

Mg(OH)2
molar mass= 58.33 g/mol

Question 20

When potassium nitrate is heated, potassium oxide, nitrogen gas, and oxygen are formed:
4 KNO3(s) → 2 K2O(s) + 2 N2(g) + 5 O2(g). I
How many grams of potassium nitrate must be heated to produce 74.5 g of Oxygen?

Answer 20

188g KNO3

(how to: grams O2–> mol O2 –> mol KNO3 —> Grams of KNO3)

Question 21

What is the balanced equation of NH3 + CuO (products are N2, Cu, and H2O)

Answer 21

2 NH3 (g) + 3 CuO (s) —> 1 N2(g) + 3 Cu(s) + 3 H2O (l)

Question 22

What are the values for [ α ]?
What are the values for [ n ]?
What are the values for [ γ ]?
What are the values for [ β ]?
what does the top number mean what does the bottom number mean?

Answer 22

a- 4 / 2 - alpha particle
n - 1 / 0 - neutron
γ - 0 / 0 - gamma ray
β - 0 / -1 - beta particle

top number is the mass number (positive number will take that amount away from products mass)
Bottom number are the protons (postive will take that amount AWAY from from products proton amount, MAKING IT A DIF ELEMENT!)

Question 23

Radium-223 has a half-life of about 247 hours, how many half lives would a sample of radium-223 go through during a period of 57 days?

Answer 23

5 half lives

Question 24

What gas has the higher GWP but a short lifetime in the atmosphere?

Answer 24

CH4

Question 25

What is the MOST IMPORTANT gas concerning anthropogenic climate change? Where is majority of its emissions from?

Answer 25

CO2 -- comes from fossil fuel combustion

Question 26

The radioactive decay of radium-223 involves the emission of a single alpha particle ( 4 / 2 α). Write the nuclear equation that describes that reaction....

Answer 26

223 Ra ---> 219 Rn + 4 / 2 α

Question 27

What is the product of this decay reaction: (14/6) C + (0 / -1 ) Beta particle --->

Answer 27

---> (14 / 7 ) N + ( 0 / -1) Beta particle

Question 28

Neptunium-237 decaying by alpha particle emission.

Answer 28

𝟐𝟑𝟕 Np → (4 / 2) 𝛂 + 233 𝐏𝐚

Question 29

The nuclear fission of plutonium-239 to yield xenon-134, zirconium-103, and a number of neutrons

Answer 29

(239/94) 𝐏𝐮 + (1 / 0) n --> (134/54) 𝐗𝐞 +(103/40) 𝐙𝐫 + 𝟑 (1/0) 𝐧

Question 30

What are the main ideas from the Chernobyl disaster:

Answer 30

- nuclear fission releases energy by hitting a heavy molecule (like uranium) with neutrons which will split it causing a train reaction of splitting aka energy released -cooling system malfunctioned which caused the core to get so hot that it exploded - radiation poisoning releasing 8 tons of radioactive material

Question 31

A typical nuclear power plant at can generate 750 MW of power. Determine how much energy in Joules a power plant can produce in a year assuming it is operating at full capacity

Answer 31

2.4 x 10^16 J per year

Question 32

Is photosynthesis endothermic or exothermic? Why?

Answer 32

Endothermic, it requires CONSTANT energy from the sun to form glucose and oxygen.

Question 33

Which of the following has the LEAST chemical potential energy per gram? a. ethanol b. wood c. ice cream d. coal e. carbon dioxide

Answer 33

E- carbon dioxide has the least chemical potential energy per gram

Question 34

Combustion follows this equation for amount of heat energy: q = m x CH-T (change in temperature) x c (specific heat) mass of methanol consumed: 0.463 g Mass of water in can: 104.835 g Change in temp: 21 degrees Celsius

Answer 34

19900 j/g methanol (set- up: q = 104.825 x 21 x 4.184 = 9210 J )

Question 35

How long would it take for an initial sample of 1.6g of 223-At to go down to 100mg if the half-life is 50 seconds?

Answer 35

4 half lives or 200 seconds (set-up: 100mg = 0.1 g 0.1/1.6 = 4 half-lives

Question 36

What does the bombardment of silber by neutrons produce?

Answer 36

Radioactive isotopes

Question 37

An atom of a differnt element is _____ when an alpha particle is emitted from a radioactive nucleus

Answer 37

ALWAYS formed

Question 38

Radioactive elements with short half lives are ____.

Answer 38

UNstable

Question 39

what are the catalysts and intermediates for the following reaction: 2 NO + 2 H2 → 1 N2 + 2 H2O (hint: this the overall reaction from 2 steps)

Answer 39

catalysts: NONE intermediate: N2O2 and N2O

Question 40

What is the reaction equation for the cracking reaction of hexadecane (C16H34) to produce heptane and 1 other product ...

Answer 40

---heat---> C7H16 + C9H18

Question 41

What is the percent mass of carbon in CaCO3?

Answer 41

12.01% (set up: molar weight of C = 12.01 g/mol molar weight of CaCO3= 100 g/mol ---> 12.01/100 x 100 = 12.01)

Question 42

How many moles of oxygen atoms are in 150.0 grams of calcium carbonate?

Answer 42

4.5 moles of O atoms Set-up: 150g CaCO3 x 1 mol CaCO/ 100 g x 3 moles O/ 1 mole CaCO3 = 4.5 moles

Question 43

What does “enrichment” mean with respect to uranium nuclear fuel

Answer 43

Increasing the concentration of 235-U in uranium compared to 238-U

Question 44

When the unstable isotope Chromium-57 decays radioactively to form Manganese-57, what particle is emitted from the nucleus?

Answer 44

---> 57/25 Mn + 0/-1 beta particle

Question 45

Given that respiration is only 39% efficient, how many grams of sugar would we need to consume in order to generate 250 Cal of energy from respiration? ( 1 cal = 4.184 kJ; energy from sucrose = 16.4 kJ/gram)

Answer 45

164 g sugar needed (set-up: cal --> kJ --> grams grams--> 100% / 39% --> 164 g sugar needed)