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introductory chemistry atoms first

Questions and Answers of Introductory Chemistry Atoms First

The value of ΔErxn for an exothermic reaction is always negative.(a) Why is this so in terms of Ereactants versus Eproducts?(b) Why is this so in terms of bonds broken in the reactants versus bonds
For a particular chemical reaction, the absorbed energy is 800 kJ to break old bonds, and 400 kJ is released on forming new bonds. Calculate ΔErxn and comment on whether this reaction is exothermic
For a particular reaction, the absorbed energy is 800 kJ to break old bonds, and ΔErxn is equal to –800 kJ. How much energy is released into the surroundings as the product bonds are formed?
What do we mean by activation energy?
What is the relationship between the rate of a reaction and the value of Ea for the reaction?
True or false? An energy-downhill reaction can always be expected to be faster than an energy uphill reaction. Explain your answer
Use reaction-energy profiles, complete with Ea distances labeled, to show that your answer to Problem 13.51 is correct.Data from Problem 13.51True or false? An energy-downhill reaction can always be
A reaction is exothermic, with ΔErxn = –40 kJ, and the transition state is 20 kJ higher in energy than the reactants. Sketch a reaction-energy profile consistent with this information, complete
Consider the transition state for a chemical reaction.(a) What is it (define it).(b) Can there be only imminent bond breaking in a transition state? Explain.
For a particular reaction, the reactants are at 30 kJ, the products are at 60 kJ, and the transition state is at 100 kJ. Sketch a reaction energy profile showing both ΔErxn and Ea. Also, calculate
Would decreasing the size of Ea increase or decrease the rate of a reaction? Explain your choice fully
Is reaction rate directly or inversely related to Ea?
Would increasing the temperature increase or decrease the rate of a reaction? Explain your choice fully.
At a given temperature, what factors determine which reactant molecules can become product molecules?
Using reaction-energy profiles, plot two exothermic reactions that have the same ΔErxn, but make one reaction substantially faster than the other. Label the plots “fast” and “slow,” and
Reactions go faster when heated. A student claims this is because as temperature increases, the activation energy Ea for a reaction decreases. Is this student correct or incorrect? If incorrect, then
Why might one reaction have a much larger Ea than another reaction?
What is the rule of thumb for how reaction rate changes as the temperature changes?
How can the orientation of reactant molecules as they collide play a role in substitution reactions?
If there were no orientation requirement for collisions, would reactions be faster or slower than they are? Explain your answer.
What is a catalyst and why is so little catalyst needed to get the desired effect?
In the substitution reaction of Cl– for OH– in 2-propanol, explain how Zn2+ acts as a catalyst to increase the reaction rate.
What is the general name given to biological catalysts?
What is meant by the following terms:(a) Substrate(b) Active site(c) Lock-and-key mechanism
Inhibitors are poisons that permanently stop a catalyst or an enzyme from working. Postulate how they might accomplish this.
The development of the first antibiotics was described. Was this accomplished by making modified versions of the lock or the key? Explain your answer.
Why are catalysts important to industrial chemical processes? Why are they important to biological chemical processes?
The productis often called the “inherent rate” of a reaction. Why? Fraction of collisions with energy equal to or greater than Ea x Fraction of collisions in which molecules have proper
In general, increasing the concentration of a reactant will usually increase the rate of a reaction. Why is this true?
Why would decreasing the volume of a container in which a gas-phase reaction is taking place speed up the reaction?
Does the rate constant k increase, decrease, or stay the same when:(a) You increase the temperature (explain your choice fully).(b) You add a catalyst (explain your choice fully).
Suppose you increase the temperature of a reaction from 100°C to 200°C and the reaction gets three times as fast.(a) Would the rate constant for the reaction at 100°C be equal to the rate constant
The rate of a reaction depends both on inherent factors and on concentration. The rate constant k is associated with the inherent factors. What are they?
A student says that an exothermic reaction will always have a larger rate constant k than an endothermic one and will thus always be faster. What is wrong with her line of reasoning?
Given the general form of the rate law, Rate = k[Reactant 1]x[Reactant 2]y answer the following questions:(a) Which part of the rate law reflects the inherent factors of the reaction?(b) What is the
True or false?(a) The orders x and y in a rate law are written directly from the balancing coefficients from the balanced equation for a reaction.(b) The overall order of a reaction is the sum of the
How do we go about determining the orders in an experimental rate law? Use the term “kinetics experiments” in your answer, defining what those are.
If a reaction rate has a first-order dependence on a given reactant concentration, what will happen to the rate when the concentration of that reactant is doubled?
If a reaction rate has a second-order dependence on a given reactant concentration, what will happen to the rate when the concentration of that reactant is doubled?
The reaction A + 2B + C → AB2C has a rate that does not change when more C is added to the reaction flask. Suppose the overall reaction order is 2, and the reaction is first-order with respect to
A reaction A + B → Product is run in a balloon. (Both A and B are gases.) The balloon has a volume of 1 L and is initially loaded with 1 mole of A and 1 mole of B. The reaction has the rate law
Repeat Problem 13.87 for a reaction that has the rate law Rate = k[A]2Data from Problem 13.87A reaction A + B → Product is run in a balloon. (Both A and B are gases.) The balloon has a volume of 1
Repeat Problem 13.87 for a reaction that has the rate law Rate = k[A][B]2Data from Problem 13.87A reaction A + B → Product is run in a balloon. (Both A and B are gases.) The balloon has a volume of
Repeat Problem 13.87 for a reaction that has the rate lawRate = k[A][B]Data from Problem 13.87A reaction A + B → Product is run in a balloon. (Both A and B are gases.) The balloon has a volume of 1
Given the rate data below from a series of kinetics experiments, determine the orders for the following reaction, and state the overall order of the reaction: H,O2(aq)+3I
A student measures the rate of a reaction by measuring how much the concentration of one of the reactants changed over a period of 5 s. She writes in her lab book that the reaction rate is 2.00 ×
In a kinetic study of the reaction 2A(g) + B(g) → P(g) the following rate data were obtained. Write the rate law with proper orders. Give the overall order of the reaction. Finally, state what this
In a kinetic study of the reactionthe following rate data were obtained. Write a rate law complete with proper values for the orders. What is the overall order of the reaction? 2 C10₂(aq)+ 2 OH
Does the following reaction-energy profile represent an endothermic or exothermic reaction in the forward direction? In the reverse direction? Energy,
What is ΔEforward rxn for the reaction in Problem 13.95? What is ΔEreverse rxn?Data from Problem 13.95Does the following reaction-energy profile represent an endothermic or exothermic reaction in
What is the activation energy for the forward reaction in Problem 13.95?Data from Problem 13.95Does the following reaction-energy profile represent an endothermic or exothermic reaction in the
What is the activation energy for the reverse reaction in Problem 13.95?Data from Problem 13.95Does the following reaction-energy profile represent an endothermic or exothermic reaction in the
From the following reaction-energy profiles, determine whether reactions A and B are exothermic or endothermic in the forward direction: Energy,
Which of the following will slow down a chemical reaction?(a) Increase concentration of reactants.(b) Add catalyst.(c) Decrease temperature.(d) All of the above.
What are ΔEforward rxn for reactions A and B in Problem 13.100?Data from Problem 13-100From the following reaction-energy profiles, determine whether reactions A and B are exothermic or endothermic
What are the forward-direction activation energies for reactions A and B in Problem 13.100? What are the reverse-direction activation energies?Data from Problem 13-100From the following
Assuming the reaction conditions (temperature, concentrations, and so on) are the same, compare the forward-direction rates for reactions A and B in Problem 13.100.Data from Problem 13-100From the
The mechanism for the endothermic reaction(a) Draw the reaction-energy profile for this reaction and label reactants, products, reaction intermediates, transition states, activation energies, and
The rate constant k of a chemical reaction can be changed by (a) Changing the temperature at which the reaction is run (b) Changing the concentration of reactants (c) Adding a catalyst (d) All of
In each reaction, indicate which bonds are broken and which bonds are formed: (a) N₂ + 3H₂ → 2 NH3 (b) PC15 PCl3 + Cl₂ (c) H₂+2 ICI→ 2 HCl + 1₂ (d) 4 HBr + O₂ → 2 H₂O + 2Br2
Indicate whether each reaction is endothermic or exothermic: (a) CO₂ + 2 H₂OCH4 +2O₂ AErxn = +890 kJ (b) CH4 + 2O₂ →CO₂ + 2 H₂O AErx = -890 kJ (c) S + O₂ SO₂ + Heat (d) N₂+ 3
Fill in the blanks.When a chemical reaction is in the _______ _______ , the reactant bonds are just ready to break and the product bonds are just ready to form.
Determine the value of k for a reaction for which:(a) The fraction of collisions having energy > Ea is 0.42 and the fraction of collisions having the proper orientation is 0.15.(b) The fraction of
The experimental rate law for the reaction(a) Show that each mechanism results in the correct overall reaction.(b) Which mechanism is consistent with the rate law?(c) Why does BC appear in the rate
The rate law for the reaction 2NO + Br2 → 2 NOBr is Rate = k[NO]2 [Br2]. How will the rate change when:(a) [NO] is doubled?(b) [Br2] is tripled?(c) [NO] is tripled?(d) [Br2] is quadrupled?(e) [NO]
Fill in the blanks.The slowest step in a reaction mechanism is called the _______-_______ step.
Fill in the blanks.For a reaction mechanism to be valid, the _______ rate law must agree with the _______ rate law.
Determine the value of Ea and ΔErxn for each case below. Also indicate whether each reaction is endothermic or exothermic. (a) (b) (c) (d) Energy of reactants, kJ 100 100 50 20 Energy of Energy
ΔErxn for the reaction XSY is +30 kJ.(a) Is the reaction endothermic or exothermic?(b) Rewrite the reaction showing heat as either a reactant or a product.(c) What is the value of ΔErxn for the
Which of the following are substitution reactions: (a) CH3Br + I¯→CH₂I + Br (b) H₂ + Br2 → 2 HBr (c) (d) - CH, = CH, + H,→CH → CH3 CH3CH₂Cl + OH¯ →CH₂CH₂OH + CI
The reaction N2 + 3H2 → 2 NH3 is exothermic. Draw a reaction-energy profile for the reaction. Label the gap that represents ΔErxn.
True or false? A catalyst in a reaction decreases the energy gap between reactants and products. If the statement is false, explain why
The mechanism for the reaction of A2 with B is:(a) Write the overall reaction that is occurring.(b) Which step determines the rate law for the reaction?(c) Write the rate law for the reaction.(d)
The rate law for a reaction involving A(g) as the only reactant is: Rate = k[A]2 What happens to the rate when:(a) The volume of the reaction container is halved?(b) The concentration of A is tripled?
Explain why this statement is false: A reaction in which weak bonds are broken and strong bonds are formed is an endothermic reaction.
Indicate whether each of the following statements is true or false. Rewrite each false statement to make it true.(a) Raising the temperature of a reaction mixture increases the number of reactant
Which reaction occurs fastest, one with Ea = 20 kJ, one with Ea = 50 kJ, or one with Ea = 75 kJ
The general rate law for a reaction is: Rate = k[H2]x[Cl2]y Write a reaction for which this general rate law is correct.
A student says to you, “Catalysts are not used up in chemical reactions because they are not involved in the reactions.” Is this statement true or false? Why?
Explain the difference between the energy factor and the orientation factor in the equation for reaction rate (Equation 13.1).Equation 13.1 Reaction rate Number of collisions per Fraction of
Explain the difference between a reaction intermediate and a catalyst in terms of the order in which each appears in the various steps of a reaction mechanism.
Write the general rate law for each reaction, using x and y exponents as orders:(a) 2NO + O2 → 2NO2(b) 2H2O2 → 2H2O + O2
Chemical companies invest a considerable amount of time and energy in search of better catalysts for their chemical processes. Explain how this investment might pay off.
A reaction releases 900 kJ of energy.(a) Is the reaction endothermic or exothermic?(b) Which are higher in the reaction-energy profile, reactants or products? Explain.(c) Does this reaction go uphill
Indicate whether each statement is true or false. Rewrite each false statement to make it true.(a) The exponents in the rate law for a reaction that has a one-step mechanism can be determined from
Explain why the value of k gets larger as the temperature of a reaction mixture is increased.
Consider the decomposition reaction of ozone into oxygen: 2O3(g) → 3O2(g) Suppose the mechanism for this reaction is just the collision between two ozone molecules, as shown in the following
Consider the basic hydrolysis (reaction with aqueous base) of (CH3)3CBr.The rate law is first order with respect to (CH3)3CBr and zero order with respect to OH–. What does this imply about the
Consider the decomposition of ozone (O3) to oxygen (O2).The rate law for this reaction is: Rate = k[O3]2/[O2]. How is the rate of this reaction affected by the concentration of oxygen? 203(g)
The following is a two-step mechanism for how chlorine atoms in the upper atmosphere react with and decompose ozone.According to the mechanism, which is the intermediate and which is the catalyst?
A student claims that an endothermic reaction will always have a higher activation energy than an exothermic reaction, because an endothermic reaction ends up with the products at a higher energy
Ace chemistry student Sidney Einstein (no relation) was carrying out a kinetics experiment in lab which produces iodine and uses starch as an indicator. In the first minute after mixing, Sidney
Why is it unlikely that the reaction A + 2 B + C → P occurs in one step?
True or false? The orders in a rate law are equal to the balancing coefficients in the slowest elementary step in a mechanism.
Suppose the reaction in Problem 13.144 did occur in one step. What rate law would predict such a mechanism?Data from Problem 13.144Why is it unlikely that the reaction A + 2 B + C → P occurs in one
Why can we ignore other steps and use only the rate-determining step in a mechanism to write the predicted rate law?
Is it wise to postulate a three-molecule collision as an elementary step in a reaction mechanism? Explain your answer.
Suppose a postulated reaction mechanism generates a rate law that does not agree with the experimentally determined rate law. What does this say about the postulated mechanism?
Suppose a postulated mechanism does generate the experimental rate law, but the elementary steps, when added together, do not generate the balanced equation for the overall reaction. What can you say
Suppose a postulated mechanism does generate the experimental rate law, and when the elementary steps are added together, the balanced equation for the overall reaction is generated. What can you say

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