Topic 11 Lesson 1 HW

What is required for a chemical reaction to occur?

• standard temperature and pressure

• a catalyst added to the reaction system

• effective collisions between reactant particles

• an equal number of moles of reactants and products

Answer explanation

For a chemical reaction to occur, effective collisions between reactant particles are essential. This means that particles must collide with sufficient energy and proper orientation to break bonds and form new ones.

According to which theory or law is a chemical reaction most likely to occur when two particles with the proper energy and orientation interact with each other?

• atomic theory

• collision theory

• combined gas law

• law of conservation of matter

Answer explanation

Collision theory states that a chemical reaction occurs when particles collide with sufficient energy and the correct orientation. This makes it the correct choice for explaining when reactions are likely to happen.

Two reactant particles collide with proper orientation. The collision will be effective if the particles have

• high activation energy

• high ionization energy

• sufficient kinetic energy

• sufficient potential energy

Answer explanation

The collision will be effective if the particles have sufficient kinetic energy, as this energy allows them to overcome the activation energy barrier and react. High activation energy or ionization energy is not directly relevant.

As the number of effective collisions between reacting particles increases, the rate of reaction

• decreases

• increases

• remains the same

Answer explanation

As the number of effective collisions between reacting particles increases, more particles can react with each other, leading to a higher rate of reaction. Therefore, the correct answer is that the rate of reaction increases.

As the temperature of a reaction increases, it is expected that the reacting particles collide

• more often and with greater force

• more often and with less force

• less often and with greater force

• less often and with less force

Answer explanation

As temperature increases, particles gain kinetic energy, leading to more frequent collisions and greater force during those collisions. This enhances the likelihood of successful reactions, making 'more often and with greater force' the correct choice.

A 1.0-gram piece of zinc reacts with 5 milliliters of HCl(aq). Which of these conditions of concentration and temperature would produce the greatest rate of reaction?

• 1.0 M HCl(aq) at 20°C

• 1.0 M HCl(aq) at 40°C

• 2.0 M HCl(aq) at 20°C

• 2.0 M HCl(aq) at 40°C

Answer explanation

The greatest rate of reaction occurs with higher concentration and temperature. 2.0 M HCl(aq) at 40°C provides both increased reactant concentration and higher kinetic energy, leading to more frequent and effective collisions.

A 5.0-gram sample of zinc and a 50.-milliliter sample of hydrochloric acid are used in a chemical reaction. Which combination of these samples has the fastest reaction rate?

• a zinc strip and 1.0 M HCl(aq)

• a zinc strip and 3.0 M HCl(aq)

• zinc powder and 1.0 M HCl(aq)

• zinc powder and 3.0 M HCl(aq)

Answer explanation

The reaction rate is fastest with zinc powder due to its larger surface area, and 3.0 M HCl provides a higher concentration of reactants, increasing the reaction rate compared to other combinations.

A catalyst increases the rate of a chemical reaction by

• providing an alternate reaction pathway

• providing the required heat of reaction

• increasing the potential energy of the products

• increasing the activation energy of the reaction

Answer explanation

A catalyst increases the rate of a chemical reaction by providing an alternate reaction pathway, which lowers the activation energy needed for the reaction to occur, thus speeding it up.

Given the reaction: A + B → C + D

The reaction will most likely occur at the greatest rate if A and B represent

• nonpolar molecular compounds in the solid phase

• ionic compounds in the solid phase

• solutions of nonpolar molecular compounds

• solutions of ionic compounds

Answer explanation

The reaction A + B → C + D will occur at the greatest rate in solutions of ionic compounds because they dissociate into ions, increasing the frequency of effective collisions compared to solid or nonpolar phases.

Given the reaction at 25°C: Zn(s) + 2 HCl(aq) ZnCl₂(aq) + H₂(g)

The rate of this reaction can be increased by using 5.0 grams of powdered zinc instead of a 5.0-gram strip of zinc because the powdered zinc has

• 
  lower kinetic energy

• 
  lower concentration

• more surface area

• more zinc atoms

Answer explanation

The rate of the reaction increases with powdered zinc because it has more surface area compared to a strip. This allows more collisions between zinc and HCl, enhancing the reaction rate.