1. A substance decomposes in a first-order reaction with a rate constant of 6.70

Question

1. A substance decomposes in a first-order reaction with a rate constant of 6.70 x 10–4 s –1 . If the initial concentration of the substance is 1.50 M, what is its concentration after 500. s?

Please show all work and explain

2. Which statements about the behavior of gaseous H2 molecules in a container at 1 atm and 298 K are correct?

I. All H2 molecules are moving at the same speed.

II. The H2 molecules are colliding more frequently with the walls of the container than they would in the same container at 398 K.

I don't understand why neither of the statements are correct.

3. In a well-insulated vessel, 50.0 g ice at 0.0 ºC is added to 350. g water at 32.0 ºC. What is the final temperature when the mixture reaches equilibrium? (The heat of fusion of ice is 334 J g–1 .)

(A) 18.0 ºC

(B) 20.6 ºC

(C) 22.0 ºC

(D) 28.0 ºC

Please show work and explain

Explanation / Answer

(1)

First order rate constant integrated equaiton,

k = (1/t)* ln[A]0/[A]t

6.70 * 10-4 = (1/500.) * ln1.50/[A]t

ln1.50/[A]t =0.335

1.50 / [A]t = 1.40

[A]t = 1.07

(2)

Both are wrong. Because,

I. At a particular temperature the average kinetic energy of the gas is constant but individual molecules can have idfferet velocities.

II. Number of collissions will be high at higher temperature.But not a lower temperature.

(3)

net heat change = 0

deltaHfus + m * s * (t2-t1)ice + m * s * (t2-t1)water = 0

50.0 * 334 + 50.0 * 4.184 * (t2-0.00) + 350.*4.184*(t2-32.0) = 0

16700 + 209.2t2 + 1464.4t2 - 46860.8 = 0

1673.6 t2 = 30160.8

t2 = Final temperature = 18.00C

(A)

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