Chemistry Kinetics

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. 2nd

• B. 0th

• C. 1st

• D. 3rd

Answer explanation

The rate of the reaction changes the same as the change of the concentration of the reactant. When the reaction of the concentration doubles, the rate of the reaction doubles; therefore, the order of the reaction with respect to the reactant is 1st order.

Tags

NGSS.HS-PS1-5

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

• 3.0 M/s

• 15.0 M/s

• 5 M/s

• 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

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

• 0th

• 1st

• 2nd

• 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

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

• As a reaction proceeds, there are less products.

• As a reaction proceeds, there are less reactants.

• As a reaction proceeds the temperature decreases.

• 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.

Tags

NGSS.HS-PS1-5

Crushing a solid catalyst into finer particles before adding it to a reaction mixture will:

• Decrease the reaction rate.

• Have no effect on the reaction rate.

• Increase the reaction rate.

• Stop the reaction.

Answer explanation

Increasing the surface area of a solid reactant will increase the reaction rate by providing more area for collisions between reactant particles.

In a chemical reaction, if the concentration of reactants is increased, what happens to the reaction rate?

• It decreases

• It increases

• It remains unchanged

• It initially increases, then decreases

Tags

NGSS.HS-PS1-5

During a science fair, Abigail, Evelyn, and Priya conducted an experiment to observe the rate at which a sugar cube dissolves in water at room temperature. What is the unit of the reaction rate they observed?

• Molarity (M)

• Molarity per second (M/s)

• Kelvin (K)

• Joules (J)

Answer explanation

The unit of reaction rate in a chemical reaction is Molarity per second (M/s), which represents the change in concentration of reactants or products per unit time.

Tags

NGSS.HS-PS1-5

What is the significance of the activation energy in a chemical reaction?

• It is the energy released during the reaction

• It is the minimum energy required for reactants to transform into products

• It determines the color of the reaction mixture

• It is the energy required to break bonds in the products

In the process of baking bread, a catalyst affects the reaction by:

• Increasing the temperature of the oven.

• Decreasing the activation energy needed for the dough to rise.

• Increasing the concentration of yeast in the dough.

• Changing the equilibrium constant of the reaction.

Answer explanation

A catalyst affects a chemical reaction by decreasing the activation energy, making it easier for the reaction to occur.

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