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engineering
chemical engineering

Questions and Answers of Chemical Engineering

Indicate whether each statement is true or false. If it is false, rewrite it so that it is true. (a) If you compare two reactions with similar collision factors, the one with the larger activation
The following diagrams represent mixtures of NO(g) and O2(g). These two substances react as follows:2 NO(g) + O2(g) --†’ 2 NO2(g)It has been determined experimentally that the rate is second
Indicate whether each statement is true or false. If it is false, rewrite it so that it is true. (a) If you measure the rate constant for a reaction at different temperatures, you can calculate the
Based on their activation energies and energy changes and assuming that all collision factors are the same, which of the following reactions would be fastest and which would be slowest? Explain your
Which of the reactions in Exercise 14.61 will be fastest in the reverse direction? Which will be slowest? Explain.
(a) A certain first-order reaction has a rate constant of 2.75 × 10-2 s-1 at 20 oC. What is the value of k at 60 oC if? (b) Another first-order reaction also has a rate constant of 2.75 × 10-2 s-1
Understanding the high-temperature behavior of nitrogen oxides is essential for controlling pollution generated in automobile engines. The decomposition of nitric oxide (NO) to N2 and O2 is second
The rate of the reaction CH3COOC2H5(aq) + OHˉ (aq) → CH3COOˉ(aq) + C2H5OH(aq) Was measured at several temperatures, and the following data were collected: Temperature (oC) k (M-1
The temperature dependence of the rate constant for a reaction is tabulated as follows: Temperature (K) k (M-1
The activation energy of a certain reaction is 65.7 kJ/mol. How many times faster will the reaction occur at 50 oC than at 0 oC? State the assumptions you need to make in order to perform this
The following is a quote from an article in the August 18, 1998, issue of The New York Times about the breakdown of cellulose and starch: "A drop of 18 degrees Fahrenheit [from to 77 oF 59 oF] lowers
(a) What is meant by the term elementary reaction? (b) What is the difference between a unimolecular and a bimolecular elementary reaction? (c) What is a reaction mechanism?
A friend studies a first-order reaction and obtains the following three graphs for experiments done at two different temperatures.(a) Which two graphs represent experiments done at the same
(a) What is meant by the term molecularity? (b) Why are termolecular elementary reactions so rare? (c) What is an intermediate in a mechanism?
What are the difference between an intermediate and a transition state?
What is the molecularity of each of the following elementary reactions? Write the rate law for each. (a) CI2(g) → 2 CI(g) (b) OCIˉ(aq) + H2O CI(g) (c) NO(g) + CI2(g) → NOCI2(g)?
What is the molecularity of each of the following elementary reactions? Write the rate law for each.(a) 2 NO(g) †’ N2O2(g)(c) SO3(g) †’ SO2(g) + O(g)?
(a) Based on the following reaction profile, how many intermediates are formed in the reaction A †’ D?(b) How many transition states are there?(c) Which step is the fastest?(d) Is the
Consider the following energy profile(a) How many elementary reactions are in the reaction mechanism? (b) How many intermediates are formed in the reaction? (c) Which step is rate limiting? (d) Is
The following mechanism has been proposed for the gas-phase reaction of H2 with ICl: H2(g) + ICl(g) → HI(g) + HCl(g) HI(g) + ICl(g) → I2(g) + HCl(g) (a) Write the balanced equation for the
The decomposition of hydrogen peroxide is catalyzed by iodide ion. The catalyzed reaction is thought to proceed by a two-step mechanism: H2O2s(aq) + Iˉ (aq) → H2O(I) + IOˉ (aq) (slow) IOˉ (aq) +
The reaction 2 NO(g) + CI2(g) †’ 2 NOCI(g) was performed and the following data obtained:Is the following mechanism consistent with the data? Explain NO(g) + CI2(g) †’
(a) Given the following diagrams at t = 0 min and t = 30 min, what is the half-life of the reaction if it follows first-order kinetics?(b) After four half-life periods for a first-order reaction,
You have studied the gas-phase oxidation of HBr by O2: 4 HBr(g) + O2(g) → 2 H2O(g) + 2 Br2(g) You find the reaction to be first order with respect to HBr and first order with respect to O2. You
(a) What is a catalyst? (b) What is the difference between a homogeneous and a heterogeneous catalyst? (c) Do catalysts affect the overall enthalpy change for a reaction, the activation energy, or
(a) Most commercial heterogeneous catalysts are extremely finely divided solid materials. Why is particle size important? (b) What role does adsorption play in the action of a heterogeneous catalyst?
Platinum nanoparticles of diameter ~2 nm are important catalysts in carbon monoxide oxidation to carbon dioxide. Platinum crystallizes in a face-centered cubic arrangement with an edge length of
In solution, chemical species as simple as H+ and OHˉ can serve as catalysts for reactions. Imagine you could measure the [H+] of a solution containing an acid-catalyzed reaction as it occurs.
The oxidation of SO2 to SO3 is catalyzed by NO2. The reaction proceeds according to: NO2(g) + SO2(g) → NO(g) + SO3(g) 2 NO(g) + O2(g) → 2 NO2(g) (a) Show that the two reactions can be summed to
NO catalyzes the decomposition of N2O, possibly by the following mechanism: NO(g) + N2O(g) → N2(g) + NO2(g) 2 NO2(g) → 2 NO(g) + O2(g) (a) What is the chemical equation for the overall reaction?
Many metallic catalysts, particularly the precious-metal ones, are often deposited as very thin films on a substance of high surface area per unit mass, such as alumina (Al2O3) or silica (SiO2). (a)
(a) If you were going to build a system to check the effectiveness of automobile catalytic converters on cars, what substances would you want to look for in the car exhaust? (b) Automobile catalytic
When D2 reacts with ethylene (C2H4) in the presence of a finely divided catalyst, ethane with two deuteriums, CH2D - CH2D, is formed. (Deuterium, D, is an isotope of hydrogen of mass 2). Very little
The following diagram shows the reaction profile of a reaction. Label the components indicated by the boxes.
Heterogeneous catalysts that perform hydrogenation reactions, as illustrated in Figure 14.24, are subject to "poisoning," which shuts down their catalytic ability. Compounds of sulfur are often
(a) Explain the importance of enzymes in biological systems.(b) What chemical transformations are catalyzed (i) by the enzyme catalase, (ii) by nitrogenase?(c) Many enzymes follow this generic
There are literally thousands of enzymes at work in complex living systems such as human beings. What properties of enzymes give rise to their ability to distinguish one substrate from another?
The enzyme carbonic anhydrase catalyzes the reaction CO2(g) + H2O(l) → HCO3ˉ(aq) + H+(aq). In water, without the enzyme, the reaction proceeds with a rate constant of at 25 oC. In the presence of
The enzyme urease catalyzes the reaction of urea, (NH2CONH2), with water to produce carbon dioxide and ammonia. In water, without the enzyme, the reaction proceeds with a first-order rate constant of
The activation energy of an uncatalyzed reaction is 95 kJ/mol. The addition of a catalyst lowers the activation energy to 55 kJ/mol. Assuming that the collision factor remains the same, by what
Suppose that a certain biologically important reaction is quite slow at physiological temperature (37 oC) in the absence of a catalyst. Assuming that the collision factor remains the same, by how
Explain why rate laws generally cannot be written from balanced equation. Under what circumstance is the rate law related directly to the balanced equation for a reaction?
Hydrogen sulfide (H2S) is a common and troublesome pollutant in industrial wastewaters. One way to remove H2S is to treat the water with chlorine, in which case the following reaction occurs: H2S(aq)
The reaction is second 2 NO(g) + O2(g) → 2 NO(g) is second order in NO and first order in O2. When [NO] = 0.040 M and [O2] = 0.035 M, the observed rate of disappearance of NO is 9.3 × 10-5
(a) Identify the BrÃ¸nsted-Lowry acid and base in the reaction(b) Identify the Lewis acid and base in the reaction.
(a) The following diagram represents the reaction of PCl4+ with Cl-. Draw the lewis structures for the reactants and products, and identify the lewis acid and the lweis base in the reaction.(b) The
Which member of each pair produces the more acidic aqueous solution: (a) ZnBr2 or CdCl2, (b) CuCl or Cu(NO3)2, (c) Ca(NO3)2 or NiBr2? Explain.
Triethylamine, (C2H5)3N, has a pKb value of 2.99. Is triethylamine a stronger base than ammonia, NH3?
Indicate whether each of the following statements is correct or incorrect. For those that are incorrect, explain why they are wrong. (a) Every Brønsted-Lowry acid is also a Lewis acid. (b) Every
Use Figure 16.3 to predict whether the equilibrium lies to the right or to the left in the following reactions:
The odor of fish is due primarily to amines, especially methylamine (CH3NH2). Fish is often served with a wedge of lemon, which contains citric acid. The amine and the acid react forming a product
Hemoglobin plays a part in a series of equilibria involving protonation-deprotonation and oxygenation-deoxygenation. The overall reaction is approximately as follows:where Hb stands for hemoglobin
Calculate the pH of a solution made by adding 2.50 g of lithium oxide (Li2O) to enough water to make 1.500 L of solution.
Which of the following solutions has the higher pH? (a) A 0.1 M solution of a strong acid or a 0.1 Msolution of a weak acid, (b) A 0.1 M solution of an acid with Ka = 2 ( 10-3 or one with Ka = 8 (
What is the pH of a solution that is 2.5 ( 10-9 in NaOH? Does your answer make sense? What assumption do we normally make that is not valid in this case?
Caproic acid (C5H11COOH) is found in small amounts in coconut and palm oils and is used in making artificial flavors. A saturated solution of the acid contains 11 g/L and has a pH of 2.94. Calculate
Although HCl and H2SO4 have very different properties as pure substances, their aqueous solutions possess many common properties. List some general properties of these solutions, and explain their
Butyric acid is responsible for the foul smell of rancid butter. The pKa of butyric acid is 4.84. (a) Calculate the pKb for the butyrate ion.
Arrange the following 0.10 M solutions in order of increasing acidity (decreasing pH): (i) NH4NO3, (ii) NaNO3, (iii) CH3COONH4, (iv) NaF, (v) CH3COONa.
Many moderately large organic molecules containing basic nitrogen atoms are not very soluble in water as neutral molecules, but they are frequently much more soluble as their acid salts. Assuming
The amino acid glycine (H2N-CH2-COOH) can participate in the following equilibria in water:(a) Use the values of Ka and Kb to estimate the equilibrium constant for the intramolecular proton transfer
The structural formula for acetic acid is shown in Table 16.2. Replacing hydrogen atoms on the carbon with chlorine atoms causes an increase in acidity, as follows:
Calculate the number of H+ (aq) ions in 1.0 mL of pure water at 25 (C.
How many milliliters of concentrated hydrochloric acid solution (36.0% HCl by mass, density = 1.118 g/mL) are required to produce 10.0 L of a solution that has a pH of 2.05?
Although pure NaOH and NH3 have very different properties, their aqueous solutions possess many common properties. List some general properties of these solutions, and explain their common behavior
(a) Using dissociation constants from Appendix D, determine the value for the equilibrium constant for each of the following reactions.(b) We usually use single arrows for reactions when the forward
(a) What is the difference between the Arrhenius and the Brønsted-Lowry definitions of an acid? (b) NH3(g) and HCl(g) react to form the ionic solid NH4Cl(s). Which substance is the Brønsted-Lowry
The volume of an adult's stomach ranges from about 50 mL when empty to 1 L when full. If the stomach volume is 400 mL and its contents have a pH of 2, how many moles of H+ does the stomach contain?
Atmospheric CO2 levels have risen by nearly 20% over the past 40 years from 315 ppm to 380 ppm.(a) Given that the average pH of clean, unpolluted rain today is 5.4, determine the pH of unpolluted
In many reactions the addition of AlCl3 produces the same effect as the addition of H+. (a) Draw a Lewis structure for AlCl3 in which no atoms carry formal charges, and determine its structure using
What is the boiling point of a 0.10 M solution of NaHSO4 if the solution has a density of 1.002 g > mL?
Use average bond enthalpies from Table 8.4 to estimate the enthalpies of the following gas-phase reactions:Are both reactions exothermic? How do these values relate to the different strengths of
Cocaine is a weak organic base whose molecular formula is C17H21NO4.An aqueous solution of cocaine was found to have a pH of 8.53 and an osmotic pressure of 52.7 torr at 15 (C. Calculate Kb for
The iodate ion is reduced by sulfite according to the following reaction:The rate of this reaction is found to be first order in IO3-, first order in SO32-, and first order in H+. (a) Write the rate
(a) What is the difference between the Arrhenius and the Brønsted-Lowry definitions of a base?(b) Can a substance behave as an Arrhenius base if it does not contain an OH group?Explain.
(a) Give the conjugate base of the following Brønsted- Lowry acids: (i) HIO3, (ii) NH4+. (b) Give the conjugate acid of the following Brønsted-Lowry bases: (i) O2-, (ii) H2PO4-.
(a) Give the conjugate base of the following Brønsted-Lowry acids: (i) HCOOH, (ii) HPO42-. (b) Give the conjugate acid of the following Brønsted-Lowry bases: (i) SO42-, (ii) CH3NH2.
Designate the BrÃ¸nsted-Lowry acid and the BrÃ¸nsted-Lowry base on the left side of each of the following equations, and also designate the conjugate acid and conjugate base
Designate the BrÃ¸nsted-Lowry acid and the BrÃ¸nsted-Lowry base on the left side of each equation, and also designate the conjugate acid and conjugate base of each on the
(a) The hydrogen oxalate ion (HC2O4 -) is amphiprotic. Write a balanced chemical equation showing how it acts as an acid toward water and another equation showing how it acts as a base toward
The following diagrams represent aqueous solutions of two monoprotic acids, HA (A = X or Y). The water molecules have been omitted for clarity. (a) Which is the stronger acid, HX or HY? (b)Which is
(a) Write an equation for the reaction in which H2C6H7O5 - (aq) acts as a base in H2O(l).(b) Write an equation for the reaction in which H2C6H7O5 - (aq) acts as an acid in H2O(l). (c) What is the
Label each of the following as being a strong base, a weak base, or a species with negligible basicity. In each case write the formula of its conjugate acid, and indicate whether the conjugate acid
Label each of the following as being a strong acid, a weak acid, or a species with negligible acidity. In each case write the formula of its conjugate base, and indicate whether the conjugate base is
(a) Which of the following is the stronger Brønsted-Lowry acid, HBrO or HBr? (b) Which is the stronger Brønsted-Lowry base, F- or Cl-? Briefly explain your choices.
(a) Which of the following is the stronger Brønsted-Lowry acid, HClO3 or HClO2? (b) Which is the stronger Brønsted-Lowry base, HS- or HSO4-? Briefly explain your choices.
Predict the products of the following acid-base reactions, and predict whether the equilibrium lies to the left or to the right of the equation:
Predict the products of the following acid-base reactions, and predict whether the equilibrium lies to the left or to the right of the equation:
If a neutral solution of water, with pH = 7.00, is heated to 50 (C, the pH drops to 6.63. Does this mean that the concentration of [H+] is greater than the concentration of [OH-]? Explain.
(a) Write a chemical equation that illustrates the autoionization of water.(b) Write the expression for the ion-product constant for water, Kw.Why is [H2O] absent from this expression?
Calculate [H+] for each of the following solutions, and indicate whether the solution is acidic, basic, or neutral: (a) [OH-] = 0.00045 M; (b) [OH-] = 8.8 ( 10-9 M; (c) A solution in which [OH-] is
The following diagrams represent aqueous solutions of three acids, HX, HY, and HZ. The water molecules have been omitted for clarity, and the hydrated proton is represented as H+ rather than
Calculate [OH-] for each of the following solutions, and indicate whether the solution is acidic, basic, or neutral: (a) [H+] = 0.0505 M; (b) [H+] = 2.5 ( 10-10 M; (c) A solution in which [H+] is
At the freezing point of water (0 (C), Kw = 1.2 ( 10-15. Calculate [H+] and [OH-] for a neutral solution at this temperature.
By what factor does [H+] change for a pH change of (a) 2.00 units, (b) 0.50 units?
Consider two solutions, solution A and solution B. [H+] in solution A is 250 times greater than that in solution B. What is the difference in the pH values of the two solutions?
(a) If NaOH is added to water, how does [H+] change? How does pH change?
(a) If HNO3 is added to water, how does [OH-] change? How does pH change?
Complete the following table by calculating the missing entries and indicating whether the solution is acidic or basic.
Complete the following table by calculating the missing entries. In each case indicate whether the solution is acidic or basic.

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