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AveGali [126]
3 years ago
5

A sample of octane burns releasing 2290 J of heat to the surroundings, and the gases produced expands against a piston to do 560

joules of work. Calculate the internal energy change for this reaction.
1- –2850 J
2- –1730 J
3- –2290 J
4- +1730 J
5- +2850 J
Chemistry
1 answer:
dexar [7]3 years ago
4 0

<u>Answer:</u> The internal energy change for the reaction is -2850 J

<u>Explanation:</u>

  • <u>Sign convention of heat:</u>

When heat is absorbed, the sign of heat is taken to be positive and when heat is released, the sign of heat is taken to be negative.

  • <u>Sign convention of work:</u>

Work done for expansion process is taken as negative and work done for compression is taken as positive.

According to the First law of thermodynamics,

\Delta U=q+w

where,

\Delta U = internal energy

q = heat absorbed or released  = -2290 J

w = work done = -560 J

Putting values in above equation, we get:

\Delta U=(-2290)+(-560)\\\\\Delta U=-2850J

Hence, the internal energy change for the reaction is -2850 J

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500 mL of a solution contains 1000 mg of CaCl2. Molecular weight of CaCl2 is 110 g/mol. Specific gravity of the solution is 0. C
dangina [55]

Answer:

a) 0,2% w/v

b) r=500

c) 0,0182 M

d) 0,0145 m

e) 0,0137 equivalents

Explanation:

a) % w/v means mass of solute in grams per 100 mililiter of solution. Thus:

%w/v= \frac{1,000 g CaCl2}{500mL}×100 = 0,2%w/v

b) Ratio strength is a way to express concentration.  For w/v is in 1g of solute <em>r</em> mililiters of solution have. Thus, r = 500 because we have in the first 1 g of CaCl₂ in 500 mL of solution.

c) Molarity is moles of solute per liter of solution, thus:

1,000 g of CaCl₂ × \frac{1mol}{110g} = 9,09×10⁻³ moles of CaCl₂

500 mL of solution  × \frac{1L}{1000mL} = 0,500 L of solution

M = \frac{9,09x10^{-3} moles }{0,500 L} = 0,0182 M

d) Molality is moles of solute per kg of solution.

Specific gravity is the ratio between density of the solution and density of a reference substance (Usually water). With a specific gravity of 0,8:

kg of solution = 0,500 L of solution × \frac{0,8 kg}{1L} =<em> </em><em>0,625 kg of solution</em>

m = \frac{9,09x10^{-3}moles }{0,625 kg} = 0,0145 m

e)  In a salt, equivalents are the number of moles ables to replace one mole of charge. In CaCl₂ is ¹/₂ because with  ¹/₂ moles of CaCl₂ it is possible to replace 1 mole of charges. Thus, in 1,5 L there are:

1,5 L ×\frac{0,0182 CaCl2 moles}{1L} × \frac{1equivalent}{2 moles} = 0,0137 equivalents

I hope it helps!

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Because of river discharge, large changes in ocean salinity often occur __.
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3 years ago
What are the equilibrium concentrations of pb2+ and f– in a saturated solution of lead(ii) fluoride if the ksp of pbf2 is 3.20×1
erica [24]
Answer is:  the equilibrium concentrations fluorine anion are 0.004 M and lead cation are 0.002 M.<span>
Chemical reaction: PbF</span>₂(aq) → Pb²⁺(aq) + 2F⁻(aq).<span>
Ksp = 3,2·10</span>⁻⁸.
[Pb²⁺] = x.
[F⁻] = 2[Pb²⁺] = 2x<span>
Ksp = [Pb²</span>⁺] · [F⁻]².
Ksp = x · 4x².
3,2·10⁻⁸ = 4x³.
x = ∛3,2·10⁻⁸ ÷ 4.
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6 0
3 years ago
Read 2 more answers
What is the number of molecules of c2h5oh in a 3m solution that contains 4.00kg h2o?
Veronika [31]
 The number  of C2H5OH  in a 3 m solution that contain 4.00kg H2O is calculate as below

M = moles of the solute/Kg  of water

that is 3M = moles of solute/ 4 Kg
multiply  both side by  4

moles of the  solute  is therefore = 12  moles

by use of Avogadro law constant

1 mole =6.02 x10^23  molecules

what  about 12 moles

=12 moles/1 moles  x 6.02 x10^23 = 7.224 x10^24 molecules
3 0
3 years ago
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