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Ganezh [65]
3 years ago
9

Estimate the enthalpy change for the combustion of one mole of acetylene, C2H2, to form carbon dioxide and water vapor. BE(C?H)

= 456 kJ/mol) BE(C?C) = 962 kJ/mol BE(O=O) = 499 kJ/mol BE(C=O) = 802 kJ/mol BE(O?H) = 462 kJ/molAnswer choices:A. +653 kJ/molB. ?155 kJ/molC. +1010 kJ/molD. ?1759 kJ/molE. ?1010 kJ/mol
Chemistry
1 answer:
tia_tia [17]3 years ago
4 0

Answer:

ΔH rxn =  -1010 kJ/molC₂H₂

Explanation:

To obtain the enthalpy change for a reaction from bond energies what we do is to make an inventory of the bonds broken and formed for the balanced chemical reaction:

C₂H₂ + 5/2O₂   ⇒   2CO₂ + H₂O

Bond Broken                                    Bonds Formed

2 C-H + 1 C≡C + 5/2 O=O                4C=O + 2 H-O

Enthalpy bonds broken:

2 mol (456 kJ/mol)+ 1 mol (962 kJ/mol) + 5/2 mol (499 kJ/mol)  =  3121.5 kJ

Enthalpy bond formed:

4 mol (802 kJ/mol) + 2 mol (462 kJ/mol) = 4132.0 kJ

ΔH rxn = H broken - H formed =  3121.5 kJ - 4132.0 kJ = - 1010  kJ (per mol C₂H₂ )

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valina [46]

Left Panel

Short answer A

<em><u>Solution</u></em>

Since you have been given choices, my sloppy numbers will do, but it anyone is going to see this, YOU SHOULD CLEAN  THEM UP WITH THE NUMBERS THAT COME FROM YOUR PERIODIC TABLE.

Equation

Sodium Phosphate + Calcium Chloride ===> Sodium Chloride + Calcium Phosphate.

Na3PO4 + CaCl2 ===> NaCl + Ca3(PO4)2

<em><u>Step One</u></em>

Balance the Equation

2Na2PO4 + 3CaCl2 ==> 6NaCl + Ca3(PO4)2

<em><u>Step Two</u></em>

Find the molar mass of CaCl2

Ca = 40

2Cl = 71

Molar Mass = 40 + 71 = 111 grams/mole

<em><u>Step Three</u></em>

Find the number of moles of CaCl2

Given mass = 379.4

Molar Mass = 111

moles = given Mass / molar Mass

moles of CaCl2 = 379.4/111 = 3.418 moles

<em><u>Step Four</u></em>

Find the number of moles of Ca3(PO4)2 needed.

This requires that you use the balance numbers from the balanced equation.

For every 3 moles of CaCl2 you have, you get 1 mole of Ca3(PO4)2

n_moles of Ca3(PO4)2 = 3.418 / 3 = 1.13933 moles

<em><u>Step Five</u></em>

Find the molar mass of Ca3(PO4)2

From the periodic table,

3Ca = 3 * 40 = 120

2 P  = 2 * 31 =    62

8 O = 8 * 16   =128

Molar Mass = 120 + 62 + 128= 310 grams per mole.

<em><u>Step Six</u></em>

1 mole of Ca3(PO4)2 has a molar mass of 310 gram

1.13933 moles of Ca3(PO4)2 = x

x = 1.13933 moles * 310 grams /mole

x = 353.2 grams. As you can see, even with my rounding I'm only out 0.3 of a gram. DON'T FORGET TO PUT THIS TO THE PROPER SIG DIGS IF SOMEONE ELSE IS GOING TO SEE IT.

Middle Panel

Short Answer C

Equation

2HCl + Mg ===> H2 + MgCl2

The object of the first part of the game is to find the number of moles of H2.

<em><u>Step One</u></em>

Find the moles of HCl

1 mole HCl = 35.5 + 1 = 36.5

n = given mass divided by molar mass

n = 49 grams / 36.5 = 1.34 moles.

The balanced equation tells you that for ever mole of H2 produced, you need 2 moles of HCl. That's what the balance numbers are for.

So the number of moles of H2 is 1.34 / 2 = 0.671 moles of H2.

Now we come to Part II. We have to use an new friend of yours that I have seen only once before from you.

Find V using PV = nRT

R is going to be in kPa so the value of R = 8.314

V = ???

n = 0.671 moles

T = 25 + 273 = 298oK

P = 101.3 kPa

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V = 0.671 * 8.314 * 298 / 101.3

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Right Panel

I can't see the panel. I don't know what the problem is. Never mind I got it. I'm going to be a little skimpy on this one since I've done two like it and they are long.

LiOH + HBr ===> LiBr + H2O and the equation is balanced.

You have to figure out the moles of LiOH and HBr. Use the LOWEST number of moles

n_LiOH = given mass / molar mass = 117/(7 + 16 + 1) = 117 / 24 = 4.875 moles

n_HBr = given mass / molar mass =  141/(1 + 80) = 141 / 81 = 1.741 moles

HBr is the lower number. That's all the LiBr you are going to get is 1.741. There is no adjustment to be made from the balance equation.

n = given mass / molar mass  multiply both sides by the molar mass

n * Molar mass (LiBr) = n * (7 + 80) = 1.741 * 87 = 151 grams of

The answer is C


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