Question

5. An elementary reaction has the form 2A → B. The rate law is Rate A) k[A] B) 2 k[A] C) k? [A] D) k[A] 6. For some reaction, when concentration of reactant "A" doubles, the rate of the reaction doubles. The reaction is order in reactant A. B) 1" A oth C) 2nd D) 3rd 7. Tetrahydrofuran (commonly referred to as THF) is an organic solvent with a density of 0.889 g/mL. A solution is prepared by dissolving 11.8 g of dichlorobenzene (C6H4Cl2, MW = 147.00 g/mol) in 100.0 mL of THF. What is the molality (m) of dichlorbenzene in the THF-based solution? A) 0.903 B) 0.0889 C) 0.0803 D) 1.11 8. A 1" order reaction has a half-life of 57.3 minutes. The rate constant (k) is A) 0.0375 min B) 0.0121 min C) 18.5 sec - 1 - 1 D) 37 minutes

Answer 1

(5)

Elementary reaction:

2A --> B

Rate law:

Rate = k[A]²

(D option is correct.)

(6)

Let's say the order of the reaction is n.

Rate = k[A]ⁿ

The concentration of A double so rate is also double.

Rate' = k[2A]ⁿ = 2×Rate = 2k[A]ⁿ

2ⁿ = 2 => n = 1

(1st order reaction.)

( B option is correct.)

(7)

Density of THF = 0.889 g/mL

Mass of THF in 100.0 mL = (0.889 g/mL)(100.0 mL)

= 88.9 g = 0.0889 kg

The molar mass of dichloromethane = 147.00 g/mol

Mole of C6H4Cl2 in 11.8 g = 11.8 g/147.00 g/mol

= 0.08027 mol

Mass of solvent (THF) = 0.0889 kg

Molality = mole of solute/mass of solvent in Kg

Molality = 0.08027 mol/0.0889 kg = 0.903 m

( Molality is 0.903 m)

(A option is correct.)

(8)

Half-life (T1/2) = 57.3 minutes

Rate constant (K) = ln2/T1/2

K = ln2/57.3 minutes^-1

K = 0.0121 minutes^-1

( B option is correct.)