PCAT Chemistry 3

Question 1

The rate-determining step of a reaction is best described as:

Accepted Answer

The slowest elementary step in a mechanism

Answer

The rate-determining step is the slowest step in a reaction mechanism and controls the overall rate of the reaction.

Question 2

Which of the following is a characteristic of a Lewis acid?

Accepted Answer

It accepts an electron pair

Answer

A Lewis acid is an electron pair acceptor, which is a broader definition than the Brønsted-Lowry acid definition that requires proton donation.

Question 3

According to Hess's Law, the enthalpy change of an overall reaction:

Accepted Answer

Equals the sum of enthalpy changes of all steps

Answer

Hess's Law states that the total enthalpy change for a reaction is the sum of enthalpy changes for each individual step, regardless of the pathway.

Question 4

Which of the following molecules has a trigonal pyramidal molecular geometry?

Accepted Answer

NH3

Answer

NH3 has a trigonal pyramidal geometry because nitrogen has three bonding pairs and one lone pair, which pushes the bonds downward.

Question 5

When the pressure on a gas is doubled at constant temperature, its volume:

Accepted Answer

Is halved

Answer

According to Boyle's Law (P1V1 = P2V2), when pressure doubles at constant temperature, the volume is halved.

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