21.A concentration-time study of the gas phase reaction 2 A₃ - 3 A₂ produced the data in the table below.

 What is the concentration of A₂ after 30 seconds?
(A) 5.00 x 10*M
(B) 5.25 x 10*M
(C) 5.50 x 10*M
(D) 6.00 x 10*M

17.Which arrow represents ? (A) arrow (a) (B) arrow (b) (C) arrow (c) (D) arrow (d)

18.Which arrow represents ? (A) arrow (a) (B) arrow (b) (C) arrow (c) (D) arrow (d)

19. The following diagram shows a close-up view of the vapor pressure curves for a pure solvent and a solution containing a nonvolatile solute dissolved in this solvent. Which curve is the solvent and what happens to the vapor pressure when the solute is dissolved in the solvent? (A) Curve (a) is the solvent and the vapor pressure decreases. (B) Curve (a) is the solvent and the vapor pressure increases. (C) Curve (b) is the solvent and the vapor pressure decreases. (D) Curve (b) is the solvent and the vapor pressure increases.

20. What is the mole fraction of oxygen in a gas mixture that is 27% oxygen and 73% nitrogen by volume? (A) 0.24 (B)0.27 (C) 0.32 (D)0.37

22.The following set of data was obtained by the method of initial rates for the reaction:(A)(B)(C) (D)

23.Shown is a concentration versus time plot for a reaction involving gases A, B, and C.Which equation best represents the reaction? (A) 4A(g) - B(g) +2C(g) (B) 4A(g) +B(g) -2C(g) (C) 2C(g) →4A(g)+B(g) (D) 2C(g) +B(g)→4A(g)

24.Consider a reaction that occurs by the following one-step mechanism: A2+ B2→ 2 AB The potential energy profile for this reaction is shown below. What is the species present at reaction stage 1? (A) an intermediate (B) a product (C) a reactant (D) a transition state

25. The following set of data was obtained by the method of initial rates for the reaction:  What is the rate law for the reaction? (A) (B)(C)(D)

26.For a particular first-order reaction, it takes 48 minutes for the concentration of the reactant to decrease to 25% of its initial value. What is the value for rate constant for the reaction? (A) (B) (C)(D)

27.The reaction: 2 HI→ H2 + I2, is second order and the rate constant at 800 K is . How long will it take for 8.00 x mol/L of HI to decrease to one-fourth of its initial concentration? (A) 0.619s (B) 124 s (C) 387s (D) 429 s