Which graph represents an exothermic reaction?

For the reaction: CH3NH2(aq) + H2O(aq) ⇌ CH3NH3 +(aq) + OH- Determine the change in the pH (ΔpH) for the addition of 6.7 M CH3NH

Korolek [52]

Answer:

The change in the pH (ΔpH) is 2,17

Explanation:

The reaction:

CH₃NH₂(aq) + H₂O(aq) ⇌ CH₃NH₃⁺(aq) + OH⁻

$kb = \frac{[OH^{-}][CH_{3}NH_{3}^+]}{[CH_{3}NH_{2}]}$ (1)

In equilibrium, a solution of CH₃NH₂ 4,7M produces:

[CH₃NH₂] = 4,7 - x

[CH₃NH₃⁺] = x

[OH⁻] = x

Replacing in (1):

$4,38x10^{-4} = \frac{x^2}{4,7-x}$

x² + 4,38x10⁻⁴x - 2,0586x10⁻³ = 0

The solutions are:

x = -0,0456 No physical sense. There are not negative concentrations.

x = 0,04515 Real answer.

The concentration of [OH⁻] is 0,04515 M.

As pOH = -log [OH⁻] And pH+pOH = 14. The pH of this solution is:

pH = 12,65

The addition of 6,7M produce this changes in concentrations:

[CH₃NH₂] = 4,656 + x

[CH₃NH₃⁺] = 6,74515 - x

[OH⁻] = 0,04515 - x

Replacing in (1) you will obtain:

x² - 6,7907x + 0,3025 = 0

Solving for x:

x = 6,74586 No physical sense

x = 0,04484 Real answer.

Thus, [OH⁻] = 0,04515 - 0,044842 = 3,08x10⁻⁴M

pOH = 3,51.

pH = 10,49

Thus ΔpH is 12,65 - 10,49 = 2,16 ≈ 2,17

I hope it helps!

4 0

4 years ago

Red wavelengths are ____ theb blue wavelengths

Alex_Xolod [135]

Answer:

stronger/ brighter, thats why red is first on the rainbow

Explanation:

8 0

3 years ago

Read 2 more answers

Which car has the highest kinetic energy if each car is traveling at a speed of 1 m/s? Explain how you arrived at your answer.

KiRa [710]

Car D

Because it is the heaviest. Kinetic energy is directly proportional to the velocity and mass of the object. All the cars have the same velocity. But Car D has the most mass. So, it has most kinetic energy, because more the mass more the energy.

5 0

3 years ago

If the half-life of 37Rb is 4.7x101 years, how long would it take for 0.5 grams of a 2 gram sample to radioactively decay?

k0ka [10]

Answer: The time required will be 19.18 years

Explanation:

All the radioactive reactions follows first order kinetics.

The equation used to calculate half life for first order kinetics:

$k=\frac{0.693}{t_{1/2}}$

We are given:

$t_{1/2}=4.7\times 10^1yrs$

Putting values in above equation, we get:

$k=\frac{0.693}{4.7\times 10^1yr}=0.015yr^{-1}$

Rate law expression for first order kinetics is given by the equation:

$k=\frac{2.303}{t}\log\frac{[A_o]}{[A]}$

where,

k = rate constant = $0.015yr^{-1}$

t = time taken for decay process = ?

$[A_o]$ = initial amount of the reactant = 2 g

[A] = amount left after decay process = (2 - 0.5) = 1.5 g

Putting values in above equation, we get:

$0.015yr^{-1}=\frac{2.303}{t}\log\frac{2}{1.5}\\\\t=19.18yrs$

Hence, the time required will be 19.18 years

4 0

3 years ago

Which outcome occurs when bonds between atoms are broken or formed? A. a physical change B. an element increasing in size C. a c

snow_tiger [21]

The answer is C. Chemical change.

5 0

3 years ago

Read 2 more answers