The term mole concept is used here to determine the mass of hydrogen. The mass of hydrogen required to produce 200 g of ammonia is 35.28 g.
What is a mole?One mole of a substance is defined as that quantity of it which contains as many entities as there are atoms exactly in 12 g of carbon - 12. The formula used to calculate the number of moles is:
Number of moles = Given mass / Molar mass
The balanced equation is:
N₂ + 3H₂ → 2NH₃
3 moles of H₂ gives 2 moles of NH₃
The molecular mass of NH₃ is 17 g/mol
n = 200 / 17 = 11.76 mol
1 mole comes from 1.5 moles of H₂
So 11.76 mol comes 1.5 × 11.76 moles H₂ = 17.64 moles of H₂
Mass of H₂ = 17.64 × 2 = 35.28 g
Thus the mass of H₂ needed is 35.28 g.
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Tell how many atoms of each element are in one molecule of the substance of table salt
Answer:
Explanation:
Then, multiply the number of moles of Na by the conversion factor 6.02214179×1023 atoms Na/ 1 mol Na, with 6.02214179×1023 atoms being the number of atoms in one mole of Na (Avogadro's constant), which then allows the cancelation of moles, leaving the number of atoms of Na.Aug 15, 2020
Jill has a gel pen the gel pen has a mass of 8g and a valine of 2cm3 what is the density
Answer:
The answer is 4 g/cm³Explanation:
The density of a substance can be found by using the formula
[tex]density = \frac{mass}{volume} \\ [/tex]
From the question
mass = 8 g
volume = 2 cm³
We have
[tex]density = \frac{8}{2} \\ [/tex]
We have the final answer as
4 g/cm³Hope this helps you
PLEASE HELP!!!
The boiling point of pure water is 100 degrees Celsius. A student performs an experiment , expecting the water to boil at this temperature. However, the water does not begin boiling until 105 degrees Celsius. What can you infer from this observation ?
Answer:
The water is impure
Explanation:
Impurities raises the boiling points and lowers the melting point
calculate the density of an object with a mass of 25g and a volume of 10ml
Answer:
The answer is 2.50 g/mLExplanation:
The density of a substance can be found by using the formula
[tex]density = \frac{mass}{volume} \\[/tex]
From the question
mass = 25 g
volume = 10 mL
We have
[tex]density = \frac{25}{10} = \frac{5}{2} \\ [/tex]
We have the final answer as
2.50 g/mLHope this helps you
4.81 (a) What volume of 0.115 M HClO4 solution is needed to
neutralize 50.00 mL of 0.0875 M NaOH? (b) What volume of
0.128 M HCl is needed to neutralize 2.87 g of Mg(OH)2? (c) If
25.8 mL of an AgNO3 solution is needed to precipitate all the
cl ions in a 785-mg sample of KCl (forming AgCl), what is
the molarity of the AgNO3 solution? (d) If 45.3 mL of a 0.108
M HCl solution is needed to neutralize a solution of KOH,
how many grams of KOH must be present in the solution?
How many different flame colors were you able to detect? How many different elements must have been exposed to the flame to produce this number of colors?
Answer:
This question is incomplete
Explanation:
This question is incomplete, however, there are some basic things that be used to answer the completed question on your own. Flame test is a test that is used to identify metal ions in a compound. Although, not all metal ions produce a colour in a flame test.
In a flame test, a "clean wire loop" is dipped in an unknown solid/mixture of solids, the loop where the solids must have attached to is then placed in the tip of a blue flame (perhaps of a bunsen burner). A colour change/changes is then observed during the course of this process. Some popular metal ions and there colour in flame test are listed below
Lithium ion ⇒ red
Sodium ion ⇒ yellow
Potassium ion ⇒ lilac
Calcium ion ⇒ orange-red
Barium ion ⇒ pale-green
Copper ion ⇒ blue-green
rubidium ion ⇒ red-violet
Lead ion ⇒ gray white
The number of different colours observed will ultimately determine the number of elements exposed to the flame
Mathematically combine the three given reactions so that they sum to give a balanced chemical equation describing the production of propane, C3H8(g), from its elements, C(s,graphite) and H2(g). Show your intermediate steps. For example, if you must reverse reaction (c), write the reverse in the appropriate format; if you multiply reaction (a) by 2, write the updated equation. Make sure to enter the overall balanced equation at the bottom.
a. C3H8(g)+ 5O2(g) → 3CO2(g) + 4H2O(l)
b. C(s)+ O2(g) → CO2(g)
c. H2(g)+ 1/2O2→ H2O(l)
Answer:
The answer is in the explanation.
Explanation:
The reaction you want to obtain is:
3C(s) + 4H₂(g) → C₃H₈(g)
The sum of 3(b) + 4(c):
3b. 3C(s) + 3O₂(g) → 3CO₂
4c. 4H₂(g) + 2O₂(g) → 4H₂O(l)
3C(s) + 4H₂(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(l)
Now, this reaction -(a):
-a. 3CO₂(g) + 4H₂O(l) → C₃H₈(g) + 5O₂(g)
3C(s) + 4H₂(g) → C₃H₈(g)
Which of these statements describes a chemical property? A. Iron is attracted to a magnet. OB. Iron rusts when exposed to air. OC. Iron is a solid at room temperature. OD. Iron melts at 1538 C.
Answer: B: Iron rusts when exposed to air.
Explanation:
Answer:
B
Explanation:
OB. Iron rusts when exposed to air.
which statement about the sun is true?
A.The sun is a red giant
B. The sun will become a red giant
C. The sun began as a red giant
D. The sun cannnot become a reg giant
1. If an atom of calcium has a mass of 40:
a. Protons =
b. Neutrons =
2. If an atom of krypton has a mass of 84:
a. Protons =
b. Neutrons =
3. If an atom of tin haſ a mass of 119:
a. Protons =
b. Neutrons =
4. If an atom of tungsten has a mass of 184:
a. Protons
b. Neutrons =
Answer:
1. If an atom of calcium has a mass of 40:
a. Protons = 20
b. Neutrons = 20
2. If an atom of krypton has a mass of 84:
a. Protons = 36
b. Neutrons = 48
3. If an atom of tin has a mass of 119:
a. Protons = 50
b. Neutrons = 69
4. If an atom of tungsten has a mass of 184:
a. Protons = 74
b. Neutrons =110
In the anaerobic fermentation of grain, the yeast Saccharomyces cerevisiae digests glucose from plants to form the products ethanol and propenoic acid by the following reactions: Reaction 1: C6H12O6 2 C2H5OH + 2 CO2 Reaction 2: C6H12O6 2 C2H3CO2H + 2 H2O In an open flow reactor 4000 kg of a 12% glucose-water solution flows in. During fermentation, 120 kg of carbon dioxide is produced together with 90 kg of unreacted glucose. What are the weight percents of ethyl alcohol and propenoic acid that exit the broth? Assume that none of the glucose is assimilated into the bacteria.
Answer:
Explanation:
The first step in order to solve this particular question is to make sure that the two reactions given in the question is balanced. Therefore, we have;
Reaction 1: C6H12O6 -----------------------------> 2 C2H5OH + 2 CO2.
Reaction 2: C6H12O6 ------------------------------> 2 C2H3CO2H + 2 H2O.
Next, we determine the number of moles of water and that of glucose. Recall that we are given from the question that the open flow reactor = 4000 kg of a 12% glucose-water solution flows in that is to say the percentage for water is [100% - 12% = 88%]. Also, the molar mass of water = H₂O = 18 kg/kmol and that for glucose =180 kg/kmol.
Number of moles of water = (4000 kg × 88%) ÷ 18 = 195.6 kmol.
Number of moles of glucose= (4000kg × 12%) ÷ 180 = 2.67 kmol.
Next thing to do is to determine the number of moles in the unreacted glucose . Therefore, the 90 kg of unreacted glucose ÷ 180kg/kmol = 0.5 kmol.
So, we have that During fermentation, 120 kg of carbon dioxide is produced. Thus, the number of kmol = 120kg÷ 44kg/mol = 2.73kmol.
For reaction 1, we have 2 moles of CO₂ that is to say the extent of the reaction = 2.73kmol / 2 moles of CO₂ = 1.365 kmol.
For reaction 2, we have 2 moles of CO₂ that is to say the extent of the reaction = 2.67kmol - 0.5 kmol - 1.365kmol = 0.805 kmol.
For both reaction, the kmol for outflow of glucose = 2.73 kmol.
Also, 2 × 0.805 + 1.365 × 0 = 1.61kmol.
Hence, 195.6 kmol + 1.61 =197.21 kmol.
The mass of ethanol = 46.1 kg/kmol × 2.73 kmol = 125.853 kg.
The weight percent of ethanol has been 29.72%, and the percent mass of propionic acid has been 47.79%.
The balanced chemical equations of the reactions have been:
[tex]\rm C_6H_1_2O_6\;\rightarrow\;2\;C_2H_5OH\;+\;2\;CO_2[/tex]
[tex]\rm C_6H_1_2O_6\;\rightarrow\;2\;C_2H_3CO_2H\;+\;2\;H_2O[/tex]
The solution has consisted of 12% glucose.
Water in the solution = 88%
The mass of the solution = 4000 kg.
The moles of glucose = 12% of 4000 kg
Moles of glucose = [tex]\rm \dfrac{12}{100}\;\times\;4000\;\times\;\dfrac{1}{180\;g/mol}[/tex]
Moles of glucose = 2.67 kmol.
Moles of water = 88 % of 4000 kg
Moles of water = [tex]\rm \dfrac{88}{100}\;\times\;4000\;\times\;\dfrac{1}{18\;g/mol}[/tex]
Moles of water = 195.6 kmol.
The unreacted glucose in the mixture = 90 kg
Moles of unreacted glucose:
Moles = [tex]\rm \dfrac{weight}{molecular\;weight}[/tex]
Moles of unreacted glucose = [tex]\rm \dfrac{90\;\times\;1000\;g}{180\;g/mol}[/tex]
Moles of unreacted glucose = 0.5 kmol
The mass of carbon dioxide produced = 120 kg.
Moles of carbon dioxide produced = [tex]\rm \dfrac{120\;\times\;1000\;g}{44\;g/mol}[/tex]
Moles of carbon dioxide produced = 2.73 kmol
Since 1 mole of glucose produces 2 moles of carbon dioxide.
2.73 kmol of carbon dioxide has been produced from 1.365 kmol of glucose.
The moles of ethanol produced by reaction 1 = 2 moles/ mole glucose.
The glucose present has been 2.67 kmol.
The ethanol produced = 5.34 kmol.
Moles of propionic acid produced = 5.34 kmol.
The mass of 5.34 kmol ethanol = Moles × molecular weight
The mass of ethanol produced = 5.34 × 1000 × 46.07g/mol
The mass of ethanol produced = 246.0138 kg.
The mass of propionic acid produced = 5.34 × 1000 × 74.08 g/mol
The mass of propionic acid produced = 395.5872 kg.
The mass of water produced = 5.34 × 1000 × 18 g/mol
The mass of water produced = 96.12 kg.
The remained glucose = 90 kg
The total mass in the reactor:
= Mass of glucose + water + propionic acid + ethanol
= 90 + 96.12 + 395.5872 + 246.0138 kg
= 827.721 kg.
% Mass of ethanol = [tex]\rm \dfrac{Mass\;of\;ethanol}{Total\;mass}\;\times\;100[/tex]
% Mass of ethanol = [tex]\rm \dfrac{246.0138}{827.721}\;\times\;100[/tex]
% Mass of ethanol = 29.72%
% Mass of Propionic acid = [tex]\rm \dfrac{Mass\;of\;propionic\;acid}{Total\;mass}\;\times\;100[/tex]
% Mass of Propionic acid = [tex]\rm \dfrac{395.5872}{827.721}\;\times\;100[/tex]
% Mass of Propionic acid = 47.79 %.
The weight percent of ethanol has been 29.72%, and the percent mass of propionic acid has been 47.79%.
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How many significant figures
are in this number?
23,479
a hammer has the volume of 11.5 cubic centimeters. it also has the mass of 500 grams. what is the hammer density
Answer:
The answer is 43.48 g/cm³Explanation:
The density of a substance can be found by using the formula
[tex]density = \frac{mass}{volume} \\ [/tex]
From the question
mass = 500 g
volume = 11.5 cm³
We have
[tex]density = \frac{500}{11.5} \\ = 43.47826086...[/tex]
We have the final answer as
43.48 g/cm³Hope this helps you
Which ONE of the following has the most mass (assume they are all of the same volume)?
A block of styrofoam.
b. A block of copper.
c. A box of feathers.
d. An empty cardboard box.
Answer:
the answer is b
Explanation:
Give two examples. How does predation affect an ecosystem?
Answer:
It affects the amount of a species that may be hunted by said predator, controlled you can say.
It can cause evolution in prey that causes them to not be caught, Darwins theory in a way.
Explanation:
Explanation:
At the level of the community, predation reduces the number of individuals in the prey population. The best example of predation involve carnivorous interactions, in which one animal consumes another, Think of wolves hunting moose, owls hunting mice, or shrews hunting worms and insects.
What does Ca stand for in Italy?
The _______,
who loved knowledge and built schools to help their people learn, were
foundational in the study of science.
A.French
B.Chinese
C.Romans
D.Greeks
Explain what happens to the particles in a substance during a physical change. plllzzzzz hurry!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Answer:
When a physical change occurs, the arrangement of particles within the substance may change, but the atoms in the molecules remain bonded together.
Explanation:
Srry didn't see this till now, hope u got it right :)
Calculate the mass percent of oxygen in KMnO4.
Answer: 40.496%
Hope this helps! (:
Use the conversion factor above to find the meters in 2.7 x 103 kilometers.
1km/1000m
Answer:
2.7 × 10⁶ m
Explanation:
Step 1: Given data
Length: 2.7 × 10³ kilometers
Step 2: Convert "2.7 × 10³ kilometers" to meters
To convert a length from kilometers to meters we need the conversion factor 1 km/1000 m. We will multiply the length by the inverse of this factor so that kilometers are canceled and the final unit is meter.
2.7 × 10³ km × (1000 m/1 km) = 2.7 × 10⁶ m
2.7 × 10³ kilometers is equal to 2.7 × 10⁶ meters.
How many moles of H2 can be formed if a 4.71 g sample of Mg reacts with excess HCl?
Answer:
0.2 mole of H2.
Explanation:
We'll begin by calculating the number of mole in 4.71 g of magnesium (Mg). This can be obtained as follow:
Mass of Mg = 4.71 g
Molar mass of Mg = 24 g/mol
Mole of Mg =?
Mole = mass /Molar mass
Mole of Mg = 4.71 /24
Mole of Mg = 0.2 mole
Next, we shall write the balanced equation for the reaction.
This is illustrated below:
Mg + 2HCl —> MgCl2 + H2
From the balanced equation above,
1 mole of Mg reacted to produce 1 mole of H2.
Finally, we shall determine the number of mole of H2 produced from the reaction. This can be obtained as illustrated below:
From the balanced equation above,
1 mole of Mg reacted to produce 1 mole of H2.
Therefore, 0.2 mole of Mg will also react to produce 0.2 mole of H2.
Thus, 0.2 mole of H2 was obtained from the reaction.
The number of moles of H₂ that can be formed if a 4.71 g sample of Mg reacts with excess HCl is 0.19625 moles
Let's represent the reaction with a chemical equation
Mg + HCl → MgCl₂ + H₂
Mg + 2HCl → MgCl₂ + H₂
HCl is in excess according to the question. This means Mg is the limiting reagent and therefore determine the amount of product.
Therefore,
24 g of Mg gives 2g of H₂
4.71 g of Mg will give ? H₂
cross multiply
mass of H₂ = 4.71 × 2 / 24
mass of H₂ = 9.42 / 24 = 0.3925 g
moles of H₂ = mass / molar mass
moles of H₂ = 0.3925 / 2
moles of H₂ = 0.19625 moles
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If you blew up a balloon inside an air-conditioned house and then brought it outside on a hot summer day, then what do you expect to happen to the balloon?
Answer:
You can expect the balloon to expand a little
Explanation:
The molecules in the balloon will be heated up once they feel the warmth of the summer heat and start moving a lot faster
caed for this question.
A student reads a barometer in the laboratory and finds the prevailing atmospheric pressure to be 731 mm Hg. Express this
pressure in atmospheres, kilopascals, torrs, pounds per square inch, and pascals.
Hint: 1 atm
101.3 kPa = 760 torr = 760 mm Hg = 14.69 psi = 1.013*10Pa
mm Hg
atm
kPa
torr
psi
Pa
731
Submit Answer
Retry Entire Group
8 more group attempts remaining
Answer:
0.962 atm.
97.4 kPa.
731 torr.
14.1 psi.
97,434.6 Pa.
Explanation:
Hello.
In this case, given the available factors equaling 1 atm of pressure, each required pressure turns out:
- Atmospheres: 1 atm = 760 mmHg:
[tex]p=731mmHg*\frac{1atm}{760mmHg} =0.962atm[/tex]
- Kilopascals:: 101.3 kPa = 760 mmHg:
[tex]p=731mmHg*\frac{101.3kPa}{760mmHg} =97.4kPa[/tex]
- Torrs: 760 torr = 760 mmHg:
[tex]p=731mmHg*\frac{760 torr}{760mmHg} =731 torr[/tex]
- Pounds per square inch: 14.69 psi = 760 mmHg:
[tex]p=731mmHg*\frac{14.69}{760mmHg} =14.1psi[/tex]
- Pascals: 101300 Pa = 760 mmHg:
[tex]p=731mmHg*\frac{101300Pa}{760mmHg} \\\\p=97,434.6Pa[/tex]
Best regards.
The amount of space a material occupies is its
Answer:
—MASS is the amount of matter that makes up something. - VOLUME _ is the amount of space that a material takes up.
Explanation:
KE and PE Math
Directions: Consider a 2-kg bowling ball sits on top of a building that is 40 meters tall. It falls to the ground. Think about the amounts of potential and kinetic energy the bowling ball has:
as it sits on top of a building that is 40 meters tall.
as it is half way through a fall off a building that is 40 meters tall and travelling 19.8 meters per second.
as it is just about to hit the ground from a fall off a building that is 40 meters tall and travelling 28 meters per second.
Questions
1. Does the bowling ball have more potential energy or kinetic energy as it sit on top of the building? Why?
2. Does the bowling ball have more potential energy or kinetic energy as it is half way through its fall? Why?
3. Does the bowling ball have more potential energy or kinetic energy just before it hits the ground? Why?
4. What is the potential energy of the bowling ball as it sits on top of the building?
5. What is the potential energy of the ball as it is half way through the fall, 20 meters high?
6. What is the kinetic energy of the ball as it is half way through the fall?
What is the kinetic energy of the ball just before it hits the ground?
Answer:
1. Answer: The bowling ball has more potential energy as it sits on top of the building. It does not have any kinetic energy because it is not moving.
2. Answer: The bowling ball has equal amounts of potential and kinetic energy half way through the fall. At the half way point, half of the potential energy has been converted to kinetic energy.
3. Answer: Just before the ball hits the ground, it has more kinetic energy. As it hits the ground the potential energy becomes zero.
4. Answer:
PE=784 J
5. Answer:
PE = 392 J
6. Answer:
KE= 392 J
Also, since the PE and KE are equal at the half way point and PE =392 J, KE = 392 J.
7. What is the kinetic energy of the ball just before it hits the ground?
Answer:
KE=784 J
At first I answered in the comments, but I am able to answer now. I hope this can help
Answer:
The person above has everything, except for 2 I put " kinetic energy since it is in motion, and is picking up speed. It has already used up all of the potential energy " I don't think the potential energy and kinetic energy is equal
Explanation:
Identify the following as a weak or strong acid or base: (a) NH3, (b) H3PO4, (c) LiOH, (d) HCOOH (formic acid), (e) H2SO4, (f) HF, (g) Ba(OH)2.
Answer:
Explained
Explanation:
a) NH3- Weak Base
b) H3PO4- Weak Acid
c) LiOH- Weak Base
d) HCOOH- Weak Acid
e) H2SO4- Strong Acid
f) HF- Weak Acid
g) Ba(OH)2- Strong Base
Which of the following is a form of potential energy?
Group of answer choices
Light energy
Sound energy
Elastic energy
Kinetic energy
Answer:
elastic potential energy which is also called spring energy.
Why is the reaction of a strong acid and a strong base classified as a neutralization reaction?
a. Water and a salt are produced, leaving the pH of the solution at a very high value.
b. Only water is produced, and water has a pH of 7.0.
c. Water and a salt are produced, leaving the pH of the solution at a value of 7.0.
d. Water and a salt are produced, leaving the pH of the solution at a very low value.
Answer:
Answer choice C
Explanation:
Basicly for the Arrhenius and Bornsted-Lowery theories of acids & bases, acid-base reactions can be divided into 4 forms...
a. Strong Acid + Strong Base (HCl/NaOH) => pH = 7 at Eqv. Pt.
b. Weak Acid + Strong Base (HOAc/NaOH) => pH > 7 at Eqv. Pt.
c. Strong Acid + Weak Base (HCl & NH₄OH) => pH < 7 at Eqv. Pt.
d. Weak Acid + Weak Base (HOAc & NH₄OH) => pH ∝ Stronger Electrolyte
*HOAc = Acetic Acid
*NH₄OH = Ammonium Hydroxide
For each type reaction the pH at equivalence point depends upon the salt generated by the acid-base reaction. Ions of the salt, if they react with water, (hydrolysis) will shift the pH up or down depending upon which ion reacts. If there is no reaction by the salt ions then the pH will depend only upon autoionization of water which gives pH = 7. Typically Strong Acids + Strong Bases will give a pH = 7 at equivalence point because the ions of the salt will not undergo hydrolysis in water.
Example:
Strong Acid + Strong Base
HCl(aq) + NaOH(aq) => NaCl(aq) + H₂O(l)
NaCl(aq) => Na⁺(aq) + Cl⁻(aq)
Na⁺(aq) + H₂O(l) => No Rxn (theoretically NaOH, but NaOH is a strong base which prefers to remain 100% ionized in water).
Cl⁻(aq) + H₂O(l) => No Rxn (theoretically HCl, but HCl is a strong acid which prefers to remain 100% ionized in water).
Therefore, the net rxn is H⁺ + OH⁻ => H₂O & pH = 7.0
Weak Acid + Strong Base
HOAc(aq) + NaOH(aq) => NaOAc(aq) + H₂O(l)
NaOAc(aq) => Na⁺(aq) + OAc⁻(aq)
Na⁺(aq) + H₂O(l) => No Rxn
OAc⁻(aq) + H₂O(l) => HOAc(aq) + OH⁻(aq) => (Excess OH⁻ functions to increase pH>7 at eqv. pt.)
Strong Acid + Weak Base
HCl(aq) + NH₄OH(aq) => NH₄Cl(aq) + H₂O(l)
NH₄Cl(aq) => NH₄⁺(aq) + Cl⁻(aq)
Cl⁻(aq) + H₂O(l) => No Rxn
NH₄⁺(aq) + H₂O(l) => NH₄OH(aq) + H⁺(aq) => (Excess H⁺ functions to decrease pH < 7 at eqv. pt. )
a mechanical pencil has the mass of 55.5 grams the volume of the pencil is 11.5 cubic centimeter what is the density of the pencil
Answer:
D = M/V
Explanation:
D = 55.5g/11.5cm^3
D = 4.83g/cm^3
Octane C8H18 is an ingredient in gasoline. How many carbon atoms are in 20 kg of octane? help please
Answer:
Octane is a hydrocarbon and an alkane with the chemical formula C 8 H 18, and the condensed structural formula CH 3 (CH 2) 6 CH 3.Octane has many structural isomers that differ by the amount and location of branching in the carbon chain. One of these isomers, 2,2,4-trimethylpentane (commonly called iso-octane) is used as one of the standard values in the octane rating scale.
Chemical formula: C₈H₁₈
Molar mass: 114.232 g·mol−1
Melting point: −57.1 to −56.6 °C; −70.9 to −69.8 °F; 216.0 to 216.6 K
Solubility in water: 0.007 mg dm−3 (at 20 °C)
Answer:
Explanation:
Octane is C8H18, carbon is C. Therefore, for every mol of C8H18 there will be 8 mols of carbon.
Convert 20 kg of octane to mols octane using molar mass of octane.
Molar Mass octane = (8*12.011)+(18*1.008)=114.23 g/mol, where 8 and 18 are the atoms in the molecule and 12.011 and 1.008 are the respective molar masses of carbon and hydrogen.
20kg C8H18 *1000g/kg * mol C8H18/114.23g C8H18 = 175.1 mols octane.
Now convert that number of mols to mols carbon:
175.1 mol C8H18 * (8 mol C/mol C8H18)=1400.8 mol C.
Now remember that a mol of any given atom=6.022*10^23 atoms.
So 1400.8 mol C=1400.8*(6.022*10^23) atoms C, which is equal to your final answer, 8.4*10^26 atoms. (round to 2 significant digits since the initial number given, 20, has 2 significant digits.)
The main thing you want to look for here is your conversion factors. Once you have those down it is simple algebra from there, so be sure to practice those!