The value of DeltaH for the reaction below is +128.1 kj. CH_3OH (I) rightarrow C

Question

The value of DeltaH for the reaction below is +128.1 kj. CH_3OH (I) rightarrow CO(g) + 2H_2(g) How many kJ of heat are consumed when 15.5 g of CH_3OH (1) decomposes as shown in the equation? A) 0.48 B) 62.0 C) 1.3 x l0^2 D) 32 E)8.3 4. The specific heat of water is 4.18 J/g.K. What is the Molar Specific heat (Joules) of water? A. 8.32 B. 66.88 C. 75.24 D, 1.0 E.418.0 5 A 0.133 mol sample of gas in a 525 mL. container has a pressure of 312 torr. The temperature of the gas is degreeC. A) 20.3 B) -253 C)-20.3 D)203 F.)22.4 6. At 333 K. which of the pairs of gases below would have the most nearly identical rates of effusion? A) N_2O and NO_2 B) Co and N_2 C) N_2 and O_2 D) NO_2 and N_20_4 e) CO and CO_2 7. What is the pressure in a flat (punctured) automobile tire? A. Zero atm B. 76 Atm C. 1 Atm D. 32 PSi E. none of the above 8. If 1.0 g of each He. Ne. Ar. Kr are placed in a balloon with a small hole which gas will escape fastest? A. He B. Ne C. Ar B. D. Kr E. all will escape at the same rate 9. 6) A sample of a gas (5.0 mol) at 1.0 atm is expanded at constant temperature from 10 L to 15 L. The final pressure is atm. A) 1.5 B) 7.5 C) 0.67 D) 3.3 E) 15 10. The specific heat of metal X is twice the specific heat of metal Y. If both metals of equal mass are exposed to sun for the same length. Which of the following is true? A. X will be hotter B. Y will be hotter C. Both will be equally hot D. X will be twice as hot B. None of the above

Explanation / Answer

3. Value of deltaHrxn = 128.1 kJ / mol

15.5 g of CH3OH * (1 mol / 32.04 g) = 0.48377

So heat absorbed = 0.48377 * 128.1 = 61.97 = 62kJ

4. To pass from specific to molar specific:

4.18 J/gK * (18 g/mol) = 75.24 J/molK

5. Using Ideal Gas Law

P = 312 torr = 0.41 atm

V = 525 mL = 0.525 L

PV = nRT

0.41 atm * 0.525L = 0.133 mol * 0.082 * T

T = 19.736 K = -253.41 C

6. We use grahams law:

Rate1/Rate2 = sqrt(M2/M1)

M is molar mass

CO (28) and N2 (28) will effuse almost equally as their molar masses are almost the same.

7. Pressure in a flat and airless tire will be 1 atm, as system's pressure equalizes to that of the environment.

8. Molar masses

He = 2          Ar = 40

Ne = 20        Kr = 83.8

Comparing He and Ne

Rate Helium / Rate Neon = sqrt(20/2) = 3.16

If we compare helium to any gas, it will spread faster. So helium is the correct answer.

9. P2 = P1/(V2/V1)

P2 = 1 atm / (15/10) = 0.667 atm

10. Y will be hotter, as specific heat is the amount of heat required per unit mass to increase temperature in 1 C.

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