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Annette [7]
3 years ago
8

A certain first-order reaction (A→products) has a rate constant of 7.20×10−3 s−1 at 45 ∘C. How many minutes does it take for the

concentration of the reactant, [A], to drop to 6.25% of the original concentration?
Express your answer with the appropriate units.
Chemistry
1 answer:
lesya692 [45]3 years ago
6 0

Answer:

6,41 min

Explanation:

For the reaction:

A → products

kinetics first-order reaction law is:

ln[A] = ln[A]₀ -kt

Where [A] is concentration of reactant, [A]₀ is initital concentration of reactant, k is rate constant and t is time.

If the concentration of A is 6,25% you can assume:

[A] = 6,25; [A]₀= 100. Replacing:

ln(6,25) = ln(100) -7,20×10⁻³s⁻¹t

-2,7726 = -7,20×10⁻³s⁻¹t

385s = t

In minutes:

385s×\frac{1min}{60s} = <em>6,41 min</em>

<em></em>

I hope it helps!

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KiRa [710]

Answer:

A) 54.04%

B) 13-karat

Explanation:

A) From the problem we have

<em>1)</em> Mg + Ms = 9.40 g

<em>2)</em> Vg + Vs = 0.675 cm³

Where M stands for mass, V stands for volume, and g and s stand for gold and silver respectively.

We can rewrite the first equation using the density values:

<em>3)</em> Vg * 19.3 g/cm³ + Vs * 10.5 g/cm³ = 9.40

So now we have<em> a system of two equations</em> (2 and 3) <em>with two unknowns</em>:

We <u>express Vg in terms of Vs</u>:

  • Vg + Vs = 0.675 cm³
  • Vg = 0.675 - Vs

We <u>replace the value of Vg in equation 3</u>:

  • Vg * 19.3 + Vs * 10.5 = 9.40
  • (0.675-Vs) * 19.3 + Vs * 10.5 = 9.40
  • 13.0275 - 19.3Vs + 10.5Vs = 9.40
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  • <u>Vs = 0.412 cm³</u>

Now we <u>calculate Vg</u>:

  • Vg + Vs = 0.675 cm³
  • Vg + 0.412 cm³ = 0.675 cm³
  • Vg = 0.263 cm³

We <u>calculate Mg from Vg</u>:

  • 0.263 cm³ * 19.3 g/cm³ = 5.08 g

We calculate the mass percentage of gold:

  • 5.08 / 9.40 * 100% = 54.04%

B)

We multiply 24 by the percentage fraction:

  • 24 * 54.04/100 = 12.97-karat ≅ 13-karat
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3 years ago
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Answer:

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B. When measuring the volume, make sure to look at the graduated cylinder at eye level and read from the bottom of the meniscus.

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Answer:

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Note that;

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