For the reaction: 3BrO^{-}(aq) --> BrO_{3}^{-}(aq) + 2Br^{-}(aq)

[BrO^{- }]_{initial} is 0.60 M. 70 seconds later [BrO^{- }] is 0.12 M. What is the rate of change of [BrO^{- }] in M/s? (The brackets, [ ], indicate concentration, that is, molarity (M) or moles/liter.)

Notice that the rate of change of a reactant is negative because it is being used up.

Under a different set of conditions, the initial concentration of Br^{-} is 0.00 M. 81 seconds later it is 0.82 M. What is the rate of change of Br^{-} in M/s?

Notice that the rate of change of a product is positive because it is being produced.

Under a different set of conditions, the initial concentration of BrO_{3}^{-} is 0.23 M. 14 seconds later it is 0.83 M. What is the rate of change of BrO_{3}^{-} in M/s?

Notice that the rate of change of a product is positive because it is being produced.

Still for the reaction: 3BrO^{-}(aq) --> BrO_{3}^{-}(aq) + 2Br^{-}(aq), what is the rate of reaction in M/s, if Δ[BrO^{- }]/Δt = -0.074 M/s?

We are given the rate of change of [BrO^{- }]. Because the chemical equation has 3 moles of BrO^{- }, we must divide by 3 to get the rate of reaction.

Note that the rate of reaction is always positive.

Under a different set of conditions Δ[BrO_{3}^{-} ]/Δt = 0.029 M/s. What is the rate of reaction in M/s?

In this case, the coefficient of [BrO_{3}^{-}] is 1. Therefore:

Δ[BrO_{3}^{-} ]/Δt = Rate of reaction = .029

Note that the rate of reaction is always positive.

Under a different set of conditions Δ[Br^{- }]/Δt = 0.035 M/s. What is the rate of reaction in M/s?

Note that the rate of reaction is always positive.

If Δ[BrO_{3}^{-} ]/Δt = 0.010 M/s. What is Δ[Br^{- }]/Δt in M/s? Reminder, the rate of change [BrO_{3}^{-} ] is Δ[BrO_{3}^{-} ]/Δt.

Once again, take a look at the coefficients (molar amounts) in the chemical reaction to help you solve this one.

If Δ[BrO_{3}^{-} ]/Δt = 0.010 M/s,

then Δ[Br^{- }]/Δt = 0.010 x 2 = 0.020

If Δ[BrO_{3}^{- }]/Δt = 0.024 M/s. What is [BrO^{- }]/Δt in M/s?

Note that [BrO^{- }]/Δt is negative, because BrO^{-} is a reactant.

The rate of change of [B] is -0.243 M/min. What is the rate of reaction for the following reaction in M/min?

2A + 5B → 3C + 7D

2A + 5B → 3C + 7D

(-.0243) / -5 = .0486

Under a different set of conditions, the rate of change of [C] is 0.162 M/min. What is the rate of change of [D] in M/min? Hint given in feedback

Hint, if a = b and b = c, then a = c.

Specifically, what is the rate of reaction using [C] and what is the rate using [D]? Set the rate using [C] = the rate using [D] and solve for the rate of change of [D].

If the rate of change of [C] is 0.149 M/min. What is the rate of change of [A] in **M/s**? Hint given in feedback'

Hint. What is the rate of reaction using [C] and what is the rate using [A]? Set the rate using [C] = the rate using [A] and solve for the rate of change of [A]. Check: is the rate of change of [A] positive or negative?

Finally, units for rate of change of [A] are **M/s** not M/min. (1/min) = (1/min)(1 min/60 s).

For the reaction 2A +3B → C + 4D

The rate of reaction = k[A]^{0.5}[B]^{2}

Which of the following statements are true?

Select one or more:

To determine order of a particular reactant, look at its superscript.

To determine overall reaction rate order, find the sum of superscripts.

For a new reaction with reactant "A", suppose the rate of reaction is 0.04 M/sec when [A] = 0.23 M. The concentration of A is doubled to 0.46 M. Match the rate of reaction to the reaction order.

Rate is still 0.04 M/s | |

Rate is 0.04 x 2^{0.5} = 0.057 M/s | |

Rate is 0.04 x 2^{1} = 0.08 M/s | |

Rate is 0.04 x 2^{2} = 0.16 M/s |

Here we are essentially comparing the relative amount of change in concentration (∆[A]) to the relative amount of change in reaction rate in order to find the reaction order.

Note that K (rate constant) cancels out in each equation.

Answer 1:

Answer 2:

Answer 3:

Answer 4:

For the reaction 2NO_{2}(g) → 2NO(g) + O_{2}(g)

the following experimental data was obtained for the rate:

What is the reaction rate order? Hint given in feedback.

the following experimental data was obtained for the rate:

Run | [NO_{2}] (M) | Rate (M/s) |
---|---|---|

1 | 0.16 | 0.27 |

2 | 0.32 | 1.08 |

3 | 0.64 | 4.32 |

What is the reaction rate order? Hint given in feedback.

Select one:

Hint, what happens to the reaction rate when the reactant concentration is doubled?

What is k? Hint given in feedback

Substitute the data from one of the runs into the appropriate equation and solve for k.

For zero-order, the rate of reaction = k[NO_{2}]^{0} = k.

For first-order, the rate of reaction = k[NO_{2}]^{1}

For one half-order, the rate of reaction = k[NO_{2}]^{0.5}

For second-order, the rate of reaction = k[NO_{2}]^{2}

What is the rate when [NO_{2}] = 0.121 M?

Hint given in feedback

Hint given in feedback

Use the rate equation for the correct order with the k that you determined.

For the reaction 2H_{2}O_{2}(aq) → 2H_{2}O(l) + O_{2}(g)

the following experimental data was obtained for the rate:

What is the reaction rate order? Hint given in feedback

the following experimental data was obtained for the rate:

Run | [H_{2}O_{2}] (M) | Rate (M/s) |
---|---|---|

1 | 0.043 | 0.19 |

2 | 0.065 | 0.29 |

3 | 0.086 | 0.38 |

What is the reaction rate order? Hint given in feedback

Select one:

It is easiest to use the first and third run to determine the order.

What is k? Hint given in feedback

Substitute the data from one of the runs into the appropriate equation and solve for k.

For zero-order, the rate of reaction = k[H_{2}O_{2}]^{0} = k.

For first-order, the rate of reaction = k[H_{2}O_{2}]^{1}

For one half-order, the rate of reaction = k[H_{2}O_{2}]^{0.5}

For second-order, the rate of reaction = k[H_{2}O_{2}]^{2}

What are the units of k?

Select one:

What is the rate when [H_{2}O_{2}] = 0.082 M?

Hint given in feedback

Hint given in feedback

Use the rate equation for the correct order with the k that you determined.

^{}

For the reaction 2A(g) + 3B(g) → C(g) + 2D(g)

the following experimental data was obtained for the rate:

The rate of reaction = kA^{x}B^{y}. What is x? Hint given in feedback

the following experimental data was obtained for the rate:

Run | [A] (M) | [B] (M) | Rate (M/min) |
---|---|---|---|

1 | 0.01 | 0.2 | 2.2 |

2 | 0.01 | 0.4 | 4.4 |

3 | 0.02 | 0.4 | 8.8 |

The rate of reaction = kA

Hint: Notice that in run #2 and #3 the concentration of B does not change. So, it does not change the rate. Therefore, you can use these runs to find the order of the reaction with respect to A. In what two runs is the concentration of A the same? Use these runs to find the order of the reaction with respect to B.

From run 2 to 3, [A] doubles. Rate also doubles. This means that x=1.

What is y?

From run 1 to 2, [B] doubles. Rate also doubles. This means that y=1.

What is k?

Plug in values for a single run, as well as the x and y values determined above to solve for k.

What are the units of k?

Select one:

What is the rate when [A] = 0.043 M and [B] = 0.038 M?

Hint given in feedback

Hint given in feedback

Use the rate equation for the correct order with the k that you determined.

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Find out what the next lecture will be about and review the material ahead of time.

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