Chemistry Chapters 6
Let's assume that a gallon of gasoline contains pure octane (C8H18) and has a density of 0.700 g/mL. When octane is burned, it releases 1,303 kcal/mol of energy. How many kilocalories of energy are released from burning one gallon of gasoline?
30,200 kcal
A patient receives 2,000 mL of a glucose solution that contains 5 g of glucose in 100 mL. How many Calories does the glucose, a simple carbohydrate, contain?
400 Calories
Bicycling 10 miles per hour expends 290 Cal/h. How many chocolate chip cookies that contain 50. Cal each can you eat to equal the number of Calories used during a 1.5 h ride?
8.8 cookies
Reaction Rate
A measure of how fast a chemical reaction occurs
Calorie
A unit of energy the equals the amount of energy needed to raise the temperature of 1g of water by 1 degree C. equlas 4.184 Joules
Which of the following affect the rate of a reaction: (a) K; (b) E a; (c) temperature?
B and C
what units are used to measure energy?
Energy is measured in calories (cal) or joules (J), where 1 cal = 4.184 J. One nutritional calorie (Cal) = 1 kcal = 1,000 cal.
What is Energy?
Energy is the capacity to do work. Kinetic energy is the energy of motion, whereas potential energy is stored energy.
Potential energy
Energy that is stored
what is the difference between an endothermic and an exothermic reaction?
In an endothermic reaction, energy is absorbed, ΔH is positive (+), and the products are higher in energy than the reactants. The bonds in the reactants are stronger than the bonds in the products. In an exothermic reaction, energy is released, ΔH is negative (−), and the reactants are higher in energy than the products. The bonds in the products are stronger than the bonds in the reactants.
Forward reaction
In equilibrium, a reaction that proceeds from left to right as drawn
Energy
The capacity to do work
Active Sites
The region in an enzyme that binds a substrate, which then indergoes a very specific reaction, with an enhanced rate
Transition State
The unstable intermediate located at the top of the energy hill in a energy diagram
Carry out each of the following conversions. a)50 cal to kcal b)56 cal to kJ c)0.96 kJ to cal d)4,230 kJ to cal
a)0.05 kcal b)0.23 kJ c)230 cal d) 1.01 x 10^6 cal
Riding a bicycle at 12-13 miles per hour uses 563 Calories in an hour. Convert this value to (a) calories; (b) kilocalories; (c) joules; (d) kilojoules.
a)563,000 cal/h b)563 kcal/h c)2.36x10^6 J/h d)2,360 Kj/h
Do each of the following statements describe an endothermic or exothermic reaction? a)ΔH is a negative value. b)The energy of the reactants is lower than the energy of the products. c)Energy is absorbed in the reaction. d)The bonds in the products are stronger than the bonds in the reactants.
a)Exothermic b)Endothermic c)Endothermic d)Exothermic
How does Le Châtelier's principle predict what happens when equilibrium is disturbed?
states that a system at equilibrium reacts in such a way as to counteract any disturbance to the equilibrium. How changes in concentration, temperature, and pressure affect equilibrium are summarized in Table 6.5. Catalysts increase the rate at which equilibrium is reached but do not alter the amount of any substance involved in the reaction.
Bond Dissociation Energy
the energy needed to break a covalent bond by equally dividing the electrons between the two atoms in the bond
Kinetic Energy
the energy of motion
What are the important features of an energy diagram?
An energy diagram illustrates the energy changes that occur during the course of a reaction. Energy is plotted on the vertical axis and reaction coordinate is plotted on the horizontal axis. The transition state is located at the top of the energy barrier that separates the reactants and products. The energy of activation is the energy difference between the reactants and the transition state. The higher the energy of activation, the slower the reaction. The difference in energy between the reactants and products is the ΔH.
Enzyme
A biological catalyst composed of one or more chains of amino acids in a very specific three demontional shape
Equilibrium Constant
A characteristic value for a reaction at a given temperature and equal to the ratio of the concentrations of the products multiplied together to the concentrations of the reactants multiplied together. Each term is a raised to a power equal to its coeffecient in the balanced chemical equation
Endothermic Reaction
A chemical reaction where delta H is positive and energy is absorbed
Law of conservation of energy
A law that states that the total energy in the universe does not change. Energy cannot be created or destroyed
Le Chatilers Principle
A principle that states that if a chemical system at equilibrium is disturbed or stressed, the system will react in the direction that counteracts the disturbance or relieves the stress
Exothermic Reaction
A reaction in which energy is released and Delta H is negative
Reversible Reaction
A reaction that can occur in either direction, from reactants to products or from products to reactants
Equilibrium
A reaction that contains forward and reverses reactions that have equal reaction rate, so the concentration of each species does not change
Energy Diagram
A schematic representation of the energy changes in a reaction, which plots energy on the vertical axis, and the progress of the reactio, the reaction coordinate- on the horizontal axis
Catalyst
A substance that increases the rate of reaction but is recovered unchanged at the end of a reaction
Joule
A unit of Measurement for energy abbreviated J
How does a catalyst affect each of the following: (a) reaction rate; (b) ΔH; (c) E a; (d) K; (e) relative energy of the reactants and products?
A) Increases reaction rate B) No effect on delta H C) Lowers the Ea D) No effect on K E) No effect on the relative energies of the reactants and products
The metabolism of glucose (molar mass 180.2 g/mol) with oxygen forms CO2 and H2O and releases 678 kcal/mol of energy. C6H12O6 (aq) +6O2 (g) <-> 6CO2 (g) + 6H2O (l) a)Are the bonds formed in the products stronger or weaker than the bonds broken in the reactants? b)How much energy is released when 4.00 mol of glucose is metabolized? c)How much energy is released when 3.00 mol of O2 reacts? d)How much energy is released when 10.0 g of glucose reacts?
A) Stronger bonds in products B) 2710 kcal C) 339 kcal D) 37.6 kcal
Which value (if any) in each pair corresponds to a faster reaction? Explain your choice. A)E a = 10 kcal or E a = 1 kcal B)K = 10 or K = 100 C)ΔH = −2 kcal/mol or ΔH = +2 kcal/mol
A) The reaction with Ea= 1 kcal will proceed faster because the energy of activation is lower B) K doesn't affect the reaction rate, so we cannot predict which reaction is faster C) One cannot predict which reaction will protect faster from delta H
Consider the gas-phase reaction of ethylene(CH2═CH2) with hydrogen to form ethane (C2H6) which occurs in the presence of a palladium catalyst . A)Write the expression for the equilibrium constant for this reaction. B)If ΔH = −28 kcal/mol, are the products or reactants higher in energy? C)Which is likely to be true about the equilibrium constant for the reaction: K > 1 or K < 1? D)How much energy is released when 20.0 g of ethylene reacts? E)What happens to the rate of the reaction if the concentration of ethylene is increased? F)What happens to the equilibrium when each of the following changes occurs: [1] an increase in [H2]; [2] a decrease in [C2H6]; [3] an increase in temperature; [4] an increase in pressure; [5] removal of the palladium catalyst?
A) [C2H6]/[H2][C2H4] B) reactants higher in energy C) K>1 D) 20 kcal E) Increase in rate F) 1,2,4- Favor shift to right 3- favor shift to left 5-no change, but reduces rate of reaciton
C(s)+O2(g) ->CO2(g) The combustion of coal with oxygen forms CO2 and releases 94 kcal of energy. A)How much energy is released when 2.5 mol of C reacts? B)How much energy is released when 3.0 mol of O2 reacts? C)How much energy is released when 25.0 g of C reacts?
A)240 kcal B)280 kcal C)2.0x10^2 kcal
Consider the endothermic conversion of oxygen to ozone: 3 O2 (g) <-> 2 O3 (g) What effect does each of the following changes have on the direction of equilibrium? A)decrease [O3] B)decrease [O2] C)increase [O3] D)decrease temperature E)add a catalyst F)increase pressure
A, F- Favor shift to the right B,C,D- Favor shift to the left E- No change
Consider the exothermic reaction: . What effect does each of the following changes have on the direction of equilibrium? A)increase [C2H4] B)decrease [Cl2] C)decrease [C2H4Cl2] D)decrease pressure E)increase temperature F)decrease temperature
A,C,F - Favor shift to the right B,D,E - Favor shift to the left
What are the basic features of equilibrium?
At equilibrium, the rates of the forward and reverse reactions in a reversible reaction are equal and the net concentrations of all substances do not change. The equilibrium constant for a reaction Aa+Bb-Cc+Dd is written as K = ([C]c[D]d)/([A]a[B]b). The magnitude of K tells the relative amount of reactants and products. When K > 1, the products are favored; when K < 1, the reactants are favored; when K ≈ 1, both reactants and products are present at equilibrium.
Reverse Reaction
In equilibrium, a reaction that proceeds from right to left as drawn
State two reasons why increasing temperature increases reaction rate.
Increasing temperature increases the number of collisions. Since the average Kinetic energy of the colliding molecules is larger, more collisions are effective at causing reaction
How can the principles that describe equilibrium and reaction rates be used to understand the regulation of body temperature?
Increasing temperature increases the rates of the reactions in the body. When temperature is increased, the body dissipates excess heat by dilating blood vessels and sweating. When temperature is decreased, blood vessels constrict to conserve heat, and the body shivers to generate more heat.
How do temperature, concentration, and catalysts affect the rate of a reaction?
Increasing the temperature and concentration increases the reaction rate. A catalyst speeds up the rate of a reaction without affecting the energies of the reactants and products. Enzymes are biological catalysts that increase the rate of reactions in living organisms. Catalytic converters use a catalyst to convert automobile engine exhaust to environmentally cleaner products.
How does collision orientation affect the rate of a reaction?
Reacting molecules must have the proper orientation for new bonds to form
Define bond dissociation energy and describe its relationship to bond strength.
The bond dissociation energy is the energy needed to break a covalent bond by equally dividing the electrons between the two atoms in the bond. The higher the bond dissociation energy, the stronger the bond.
Energy of Activation
The difference in energy between the reactants and transition state, symbolized by Ea
Enthalpy Change
The energy absorbed and released in any reaction, also called the heat of the reaction and symbolized by delta H
Heat of reaction
The energy absorbed or released in any reaction and symbolized by Delta H, also called the enthalpy change
What is the heat of reaction?
The heat of reaction, also called the enthalpy change and symbolized by ΔH, is the energy absorbed or released in a reaction.
