1answer.
Ask question
Login Signup
Ask question
All categories
  • English
  • Mathematics
  • Social Studies
  • Business
  • History
  • Health
  • Geography
  • Biology
  • Physics
  • Chemistry
  • Computers and Technology
  • Arts
  • World Languages
  • Spanish
  • French
  • German
  • Advanced Placement (AP)
  • SAT
  • Medicine
  • Law
  • Engineering
Mariana [72]
1 year ago
6

i am begging anyone to help me with this! (all tutors i've asked said they can't solve it but i need someone to help me out) - i

can get the first little bit of it so maybe we can work through it together?

Chemistry
1 answer:
9966 [12]1 year ago
5 0

First, we need to calculate how much energy we will get from this combustion.

Assuming the combustion is complete, we have the octane reacting with O₂ to form only water and CO₂, so:

C_8H_{18}+O_2\to CO_2+H_2O

We need to balance the reaction. Carbon only appear on two parts, so, we can start by it:

C_8H_{18}+O_2\to8CO_2+H_2O

Now, we balance the hydrogen:

C_8H_{18}+O_2\to8CO_2+9H_2O

And in the end, the oxygen:

C_8H_{18}+\frac{25}{2}O_2\to8CO_2+9H_2O

We can multiply all coefficients by 2 to get integer ones:

2C_8H_{18}+25O_2\to16CO_2+18H_2O

Now, we need to use the enthalpies of formation to get the enthalpy of reaction of this reaction.

The enthalpy of reaction can be calculated by adding the enthalpies of formation of the products multiplied by their stoichiometric coefficients and substracting the sum of enthalpies of formation of the reactants multiplied by their stoichiometric coefficients.

For the reactants, we have (the enthalpy of formation of pure compounds is zero, which is the case for O₂):

\begin{gathered} \Delta H\mleft\lbrace reactants\mright\rbrace=2\cdot\Delta H\mleft\lbrace C_8H_{18}\mright\rbrace+25\cdot\Delta H\mleft\lbrace O_2\mright\rbrace \\ \Delta H\lbrace reactants\rbrace=2\cdot(-250.1kJ)+25\cdot0kJ \\ \Delta H\lbrace reactants\rbrace=-500.2kJ+0kJ \\ \Delta H\lbrace reactants\rbrace=-500.2kJ \end{gathered}

For the products, we have:

\begin{gathered} \Delta H_{}\mleft\lbrace product\mright\rbrace=16\cdot\Delta H\lbrace CO_2\rbrace+18\cdot\Delta H\lbrace H_2O\rbrace \\ \Delta H_{}\lbrace product\rbrace=16\cdot(-393.5kJ)+18\cdot(-285.5kJ) \\ \Delta H_{}\lbrace product\rbrace=-6296kJ-5139kJ \\ \Delta H_{}\lbrace product\rbrace=-11435kJ \end{gathered}

Now, we substract the rectants from the produtcs:

\begin{gathered} \Delta H_r=\Delta H_{}\lbrace product\rbrace-\Delta H\lbrace reactants\rbrace \\ \Delta H_r=-11435kJ-(-500.2kJ) \\ \Delta H_r=-10934.8kJ \end{gathered}

Now, this enthalpy of reaction is for 2 moles of C₈H₁₈, so for 1 mol of C₈H₁₈ we have half this value:

\Delta H_c=\frac{1}{2}\Delta H_r=\frac{1}{2}\cdot(-10934.8kJ)=-5467.4kJ

Now, we have 100 g of C₈H₁₈, and its molar weight is approximately 114.22852 g/mol, so the number of moles in 100 g of C₈H₁₈ is:

\begin{gathered} M_{C_8H_{18}}=\frac{m_{C_8H_{18}}}{n_{C_8H_{18}}} \\ n_{C_8H_{18}}=\frac{m_{C_8H_{18}}}{M_{C_8H_{18}}}=\frac{100g}{114.22852g/mol}\approx0.875438mol \end{gathered}

Since we have approximately 0.875438 mol, and 1 mol releases -5467.4kJ when combusted, we have:

Q=-5467.4kJ/mol\cdot0.875438mol\approx-4786.37kJ

Now, for the other part, we need to calculate how much heat it is necessary to melt a mass, <em>m</em>.

First, we have to heat the ice to 0 °C, so:

\begin{gathered} Q_1=m\cdot2.010J/g.\degree C\cdot(0-(-10))\degree C \\ Q_1=m\cdot2.010J/g\cdot10 \\ Q_1=m\cdot20.10J/g \end{gathered}

Then, we need to melt all this mass, so we use the latent heat now:

Q_2=n\cdot6.03kJ/mol

Converting mass to number of moles of water we have:

\begin{gathered} M=\frac{m}{n} \\ n=\frac{m}{M}=\frac{m}{18.01528g/mol} \end{gathered}

So:

Q_2=\frac{m}{18.01528g/mol}_{}\cdot6.03kJ/mol\approx m\cdot0.334716kJ/g

Adding them, we have a total heat of:

\begin{gathered} Q_T=m\cdot20.10J/g+m\cdot0.334716kJ/g \\ Q_T=m\cdot0.02010kJ/g+m\cdot0.334716kJ/g \\ Q_T=m\cdot0.354816kJ/g \end{gathered}

Since we have a heat of 4786.37 kJ form the combustion, we input that to get the mass (the negative sign is removed because it only means that the heat is released from the reaction, but now it is absorbed by the ice):

\begin{gathered} 4786.37kJ=m\cdot0.354816kJ/g \\ m=\frac{4786.37kJ}{0.354816kJ/g}\approx13489g\approx13.5\operatorname{kg} \end{gathered}

Since we have a total of 20kg of ice, we can clculate the percent using it:

P=\frac{13.5\operatorname{kg}}{20\operatorname{kg}}=0.675=67.5\%

You might be interested in
The Heliocentric model is when the sun, planets, and stars are orbiting a stationary Earth.
Anarel [89]
False

A heliocentric is when the model is
representing the sun as the center
A geocentric says the earth is at the center of the universe
3 0
2 years ago
What did Ernest Rutherford s gold foil experiment demonstrate about atoms?
Ghella [55]
-Positively charged nucleus 
-Empty spaced
-Dense core
5 0
3 years ago
2 moles of sodium chloride are dissolved in 8 liters of water. What is its molarity (M) ?
otez555 [7]

Answer:

0.25M

Explanation:

Since molarity is defined as the amount of substance in 1 liter of a solution, and amount in chemistry refers to the number of moles, molarity can be found using the equation below:

Molarity= number of moles ÷ volume in liters

Given: number of moles= 2

Volume= 8L

∴ Molarity of NaCl

= 2 ÷8

= 0.25M

4 0
3 years ago
Which is the formula mass of Na₂SO₄? *<br> 1. 119 amu<br> 2. 125 amu<br> 3. 142 amu<br> 4. 174 amu
ANTONII [103]

Answer:

the answer is option 3.

4 0
3 years ago
Read 2 more answers
Need help please help me
Mademuasel [1]

Answer:

The answer is most likely compound a

Explanation:

Covalent compounds have low melting and boiling points and conduct electricity poorly

8 0
3 years ago
Other questions:
  • Suppose you held two magnets a short distance apart,then let go. what would happen?
    7·2 answers
  • Stainless steel is an alloy of iron, chromium, nickel, and manganese metals. If a 2.000 g sample contains 10.0% nickel, what is
    10·1 answer
  • What are clouds composed of?
    9·2 answers
  • A car rolls down a ramp. What is the force acting on the car that causes the movement down the ramp? A) acceleration B) centripe
    11·1 answer
  • How can acid rain affect organisms that live in the water?
    8·1 answer
  • One of the few xenon compounds that form is cesium xenon heptafluoride (CsXeF7). How many moles of CsXeF7 can be produced from t
    14·2 answers
  • Which climate zone is most affected by its altitude?
    9·1 answer
  • Chất tinh khiết là:
    6·1 answer
  • Various nitrogen oxides, as well as sulfur oxides, contribute to acidic rainfall through complex reaction sequences. Nitrogen an
    7·1 answer
  • Write the chemical formula for tin(ii)sulfite.. Please show working thank you
    13·1 answer
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!