Chemistry - Unit 5 – Kinetics

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1. When the rate of consumption of iron (II) is 15.0 M/s, what is the rate of production of the manganese (II) ion?

• A. 3.0 M/s

• B. 15.0 M/s

• C. 5 M/s

• D. 24.0 M/s

Answer explanation

Rates of change are stoichiometric. Therefore, since iron (II) and manganese (II) are in a 5 mol: 1 mol ratio, manganese (II) is produced at a rate of 3.0 M/s at that instant.

Tags

NGSS.HS-PS1-5

2. A reaction is found to have the following mechanism, what is the order of the overall reaction with respect to substance A_2?

• A. 0th

• B. 1st

• C. 2nd

• D. 3rd

Answer explanation

The slow step for the mechanism is the first step. This means the rate law for this elementary step is equal to the overall reaction. The slow, elementary step has 1 for the coefficient for A_2; therefore, the reaction is first order with respect to A_2.

Tags

NGSS.HS-PS1-5

3. Which of the following correctly justifies why most chemical reactions slow down as they proceed?

• A. As a reaction proceeds, there are less products.

• B. As a reaction proceeds, there are less reactants.

• C. As a reaction proceeds the temperature decreases.

• D. As a reaction proceeds it consumes the catalyst.

Answer explanation

The rate of the reaction depends on the concentration of the reactants. Because a chemical reaction consumes the reactants, the rate of the reaction decreases.

4. A reaction is represented by the equation 2X + A -> XA + X. A plot of the concentration of A versus time, shown below, was found to have a negative slope. What is the order of the reaction with respect to A?

• A. 0th

• B. 1st

• C. 2nd

• D. 3rd

Answer explanation

Since the plot of [A] versus time is linear, this indicates the reaction is 0th order with respect to A.

Tags

NGSS.HS-PS1-5

Based on the data, what is the concentration of the substance after 60 s?

• A. 0.125 M

• B. 0.032 M

• C. Need to know the order of the reaction.

• D. 0.063 M

Answer explanation

The data shows the half life of the reaction is 10 s. Therefore, by dividing the concentration given by two a sufficient number of times, one finds the concentration at 60 s to be 0.063 M.

Tags

NGSS.HS-PS1-5

6. The following data table shows the concentration of a reaction and the initial rate data. Based on the table, what is the order of the reaction with respect to the reactant?

• A. 0th

• B. 1st

• C. 2nd

• D. 3rd

Answer explanation

Since the concentration of the reactant does not affect the rate of the reaction, the order of the reaction with respect to the reactant is 0th order.

Tags

NGSS.HS-PS1-5

7. Which of the following correctly justifies why a reaction is found to occur more quickly in a solution of 1.0M HCl?

• A. The acid increases the temperature of the mixture causing the rate of collision between particles to increase.

• B. The acid provides an alternative pathway for the reaction which increases the activation energy.

• C. The acid acts as a catalyst, providing an alternative pathway for the reaction.

• D. The acid solution increases the volume of the solution, decreasing the concentration of the reactants.

Answer explanation

A catalyst is a substance that increases the rate of a reaction by providing an alternative pathway. This lowers the activation energy of the overall reaction.

Tags

NGSS.HS-PS1-5

8. A reaction is represented by the equation XA -> X + A. At a certain temperature, the rate constant is 2.5 1/M·s. What is the rate of the reaction if the initial [XA] = 1.1 M?

• A. 2.8 M/s

• B. 2.5 M/s

• C. 3.0 M/s

• D. Not enough information was provided.

Answer explanation

Based on the units for the rate constant, it's determined that the reaction is second order with respect to XA. The rate law is rate=k[XA]^2. Therefore, the rate of the reaction is rate= (2.5)(1.1)^2 = 3.0

Tags

NGSS.HS-PS1-5

9. Which of the following defines the collision theory?

• A. A reaction will only occur if the particles collide with the right amount of energy and in the right orientation.

• B. Collisions between gas particles and other particles or the wall are elastic.

• C. The energy created due to the collision between atoms in mass spectrometers.

• D. The minimum amount of energy required to initiate a chemical reaction.

Answer explanation

The collision theory states that a reaction will only occur if the reactants collide with the right amount of energy and in the right orientation.

Tags

NGSS.HS-PS2-3