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Honors Chemistry 2

Chapter 10 Study Guide

Cunnings, Fall, 2014Wilmington High School, CUSD209U

SI UNIT SYSTEM & KHDBDCM


The States of Water & Phase Changes


Unit Conversions

Another Good Diagram for Classifying Matter


Molar Heat Capacities


Standard Enthalpies of Formation

Standard Entropy Changes for some common reactions


Standard Entropies

Standard Gibbs Energies of Formation


Student Notes Guide

Chapter 1010.1: Energy Transfer

I. Energy as Heat

a. A sample can transfer energy to another sample.

b. One of the simplest ways energy is transferred is as ________________.

i. ___________________ is the energy transferred between objects that are at different

temperatures

c. Though energy has many different forms, all energy is measured in units called ______________

d. Energy is never created or destroyed.

e. The amount of energy transferred from one sample must be equal to the amount of energy

received by a second sample.

i. The total energy of the two samples remains exactly the same.

II. Temperature

a. Temperature is a measure of how ______________________ something is; specifically, a

measure of the average kinetic energy of the particles in an object.

b. When samples of different temperatures are in contact, energy is ___________________ from

the sample that has the higher temperature to the sample that has the lower temperature.

c. If no other process occurs, the temperature of a sample increases as the sample absorbs energy.

d. The temperature of a sample depends on the average ________________ of the sample’s

particles.

i. The higher the temperature of a sample is, the faster the sample’s particles move.

e. The temperature increase of a sample also depends on the mass of the sample.


III. Heat and temperature are different!!

a. Temperature is an ________________________, which means that the temperature of a sample

does not depend on the amount of the sample.

b. Heat is an _____________________________, which means that the amount of energy

transferred as heat by a sample depends on the ________________of the sample.

IV. Enthalpy: Measuring the ENERGY of a substance

a. Measuring the total amount of energy present in a sample of matter is ___________________,

but changes in energy content can be determined.

i. These changes are determined by measuring the energy that enters or leaves the sample

of matter.

1. If 73 J of energy enter a piece of silver and no change in pressure occurs, we

know that the enthalpy of the silver has__________________ by 73 J.

b. Enthalpy, which is represented by the symbol H, is the ______________________________ of a

sample.

c. Enthalpy is the sum of the ___________________ energy of a system plus the product of the

system’s volume multiplied by the pressure that the system exerts on its surroundings

d. If pressure remains constant, the enthalpy increase of a sample of matter equals the energy as

heat that is received.

i. This relationship remains true even when a chemical reaction or a change of state occurs.

e. Enthalpy includes the kinetic energy of the particles

i. The particles in a sample are in ___________________________.

1. These particles have kinetic energy.

ii. The enthalpy of a sample includes the total kinetic energy of its particles.


iii. Both the ______________________________ kinetic energies of a substance’s particles

are important to chemistry, because these quantities account for every particle’s kinetic

energy.

V. Molar Heat Capacity

a. Molar heat capacity can be used to determine the ____________________________ of a sample.

b. The molar heat capacity of a pure substance is the energy as heat needed to increase the

temperature of _________ of the substance by __________.

c. Molar heat capacity has the symbol C and the unit ____________________.

d. Molar heat capacity is accurately measured only if no other process, such as a chemical reaction,

occurs.

e. The following equation shows the relationship between heat and molar heat capacity, where q is

the heat needed to increase the temperature of n moles of a substance by T.

q = nCT

heat = (amount in moles) (molar heat capacity) (change in temperature)

i. Sample Problem A

1. Determine the energy as heat needed to increase the temperature of 10.0 mol of

mercury by 7.5 K. The value of C for mercury is 27.8 J/K•mol.


f. Molar heat capacity depends on the NUMBER OF ATOMS!

i. One mole of tungsten has a mass of ____________, while one mole of aluminum has a

mass of only about ___________.

1. You might expect that much more heat is needed to change the temperature of 1

mol W than is needed to change the temperature of 1 mol Al.

2. The molar heat capacities of all of the metals are _______________________.

3. The temperature of ____________ of any solid metal is raised ________ when

the metal absorbs about __________ of heat.

g. Molar heat capacity is related to specific heat

i. The _________________________ of a substance is represented by cp and is the energy

as heat needed to raise the temperature of one gram of substance by one Kelvin.


ii. The molar heat capacity of a substance, C, is related to moles of a substance not to the

mass of a substance.

iii. Because the ______________________ is the mass of 1 mol of a substance, the

following equation is true.

M (g/mol) cp (J/Kg) = C (J/Kmol)

(molar mass)(specific heat) = (molar heat capacity)

iv. HEAT results in disorderly particle motion

1. When a substance receives energy in the form of heat, its enthalpy ____________

and the kinetic energy of the particles that make up the substance ____________.

2. The direction in which any particle moves is not related to the direction in which

its neighboring particles move. The motions of these particles are ____________.

3. Other types of energy can produce orderly motion or _______________________

of particles.

Section 10.2: Using Enthalpy

I. Molar enthalpy change

a. Because enthalpy is the total energy of a system, it is an important quantity.

b. The only way to measure energy is through _____________________.

i. There’s no way to determine the true value of H.

ii. __________ can be measured as a change occurs.

c. The enthalpy change for one mole of a pure substance is called __________________________.


d. When a pure substance is only heated or cooled, the amount of heat involved is the same as the

enthalpy change.

H = q for the heating or cooling of substances

e. The molar enthalpy change is related to the _____________________________ by the following

equation.

molar enthalpy change = CT

molar enthalpy change = (molar heat capacity)(temperature change)

f. This equation does not apply to chemical reactions or ____________________________.

g. Calculating molar enthalpy change for heating

i. Sample problem B

1. How much does the molar enthalpy change when ice warms from 5.4C to

0.2C?


ii. Sample problem C

1. Calculate the molar enthalpy change when an aluminum can that has a

temperature of 19.2C is cooled to a temperature of 4.00C.

h. Enthalpy changes of endothermic or exothermic processes

i. Enthalpy changes can be used to determine if a process is endothermic or exothermic.

ii. Processes that have positive enthalpy changes are __________________

iii. Processes that have negative enthalpy changes are __________________

II. Enthalpy of a system of several substances

a. ____________________________ is the branch of science concerned with the energy changes

that accompany chemical and physical changes.

b. Enthalpy is one of three thermodynamic properties.

c. Writing equations for enthalpy changes

i. An equation can be written for the enthalpy change that occurs during a change of state or

a chemical reaction.

1. The following equation is for the hydrogen and bromine reaction.


2. The enthalpy change for this reaction and other chemical reactions are written

using the symbol H.

3. The ___________________ enthalpy change indicates the reaction is exothermic.

Section 10.3: Changes in enthalpy during chemical reactions

I. Changes in enthalpy accompany reactions

a. A _______________________________________during a reaction depends on many variables.

i. _______________________ is one of the most important variables.

b. To standardize the enthalpies of reactions, data are often presented for reactions in which both

reactants and products have the standard thermodynamic temperature of 25.00C or 298.15 K.

c. Chemists usually present a __________________________ value for a chemical reaction by

using the chemical equation.

d. This equation shows that when 0.5 mol of H2 reacts with 0.5 mol of Br2 to produce 1 mol HBr

and all have a temperature of 298.15 K, the enthalpy decreases by 36.4 kJ.

II. Chemical calorimetry

a. For the H2 and Br2 reaction, in which H is negative, the ____________________ of the reaction

decreases.

i. The energy is released as heat by the system.

b. If the reaction was ______________________, energy in the form of heat would be absorbed by

the system and the enthalpy would increase.


c. The experimental measurement of an enthalpy change for a reaction is called calorimetry.

i. Calorimetry is the measurement of ______________________________, such as

specific heat or latent heat

d. ___________________ reactions are always exothermic.

e. The enthalpy changes of combustion reactions are determined using a bomb calorimeter.

i. A calorimeter Is a device used to measure the _____________ absorbed or released in a

chemical or physical change

ii. A calorimeter is a sturdy, steel vessel in which the sample is ignited electrically in the

presence of high-pressure oxygen.

iii. The energy from combustion is absorbed by a _____________________________ and

by the calorimeter.

iv. The water and the other parts of the calorimeter have known specific heats.

v. A measured temperature increase can be used to calculate the ________________

released in the combustion reaction and then the enthalpy change.

f. Nutritionists use chemical calorimetry

i. Inside the pressurized oxygen atmosphere of a ______________________________,

most organic matter, including food, fabrics, and plastics, will ignite easily and burn

rapidly.

ii. Sample sizes are chosen so that there is excess oxygen during the combustion reactions.

iii. Under these conditions, the reactions go to completion and produce _________________,

water, and possibly other compounds.

g. _____________________ calorimetry is another strategy

i. Instead of using a water bath to absorb the energy generated by a chemical reaction,

adiabatic calorimetry uses an insulating vessel.


ii. The word adiabatic means “not allowing _____________ to pass through.”

1. No energy can enter or escape this type of vessel.

iii. The reaction mixture ________________ in temperature if the reaction is exothermic or

decreases in temperature if the reaction is endothermic.

iv. If the system’s specific heat is known, the __________________________ can be

calculated.

v. Adiabatic calorimetry is used for reactions that are not ignited, such as for reactions in

aqueous solution.

III. Hess’s Law

a. Any two processes that both start with the same reactants in the same state and finish with the

same products in the same state will have the same _________________________.

b. Hess’s law states that the overall enthalpy change in a reaction ______________ to the sum of

the enthalpy changes for the individual steps in the process.

c. When phosphorus is burned in excess chlorine 4 mol of phosphorus pentachloride, PCl5, is

synthesized.

d. Phosphorus pentachloride may also be prepared in a two-step process.


e. The second reaction must take place four times for each occurrence of the first reaction in the

two-step process.

f. This two-step process is more accurately described by the following equations.

g. So, the total change in enthalpy by the two-step process is as follows:

h. This enthalpy change, H, for the two-step process is the same as the enthalpy change for the

direct route of the formation of PCl5.

i. This example is in agreement with Hess’s law.

j. Using Hess’s Law and algebra

i. Chemical equations can be manipulated using rules of algebra to get a desired equation.

ii. When equations are ___________________________________, enthalpy changes must

be added or subtracted.

iii. When equations are ___________________________________, the enthalpy changes

must also be multiplied by that constant.


iv. The enthalpy of the formation of CO, when CO2 and solid carbon are reactants, is found

using the equations below.

v. You cannot simply add these equations because CO2 would not be a reactant.

vi. You subtract or reverse the second equation, carbon dioxide will be on the correct side of

the equation.

vii. Reversing an equation causes the enthalpy of the new reaction to be the negative of the

enthalpy of the original reaction.

viii. Adding the two equations gives the equation for the formation of CO by using CO2 and

C.

ix. Oxygen and carbon that appear on both sides of the equation can be canceled.


k. Standard Enthalpies of formation

i. The enthalpy change in forming 1 mol of a substance from elements in their standard

states is called the standard enthalpy of formation of the substance _____________

ii. The values of the standard enthalpies of formation for elements are 0.

iii. The following equation is used to determine the enthalpy change of a chemical reaction

from the standard enthalpies of formation.

iv. Sample Problem D

1. Calculate the standard enthalpy of formation of pentane, C5H12, using the given

information.

(1) C(s) + O2(g) CO2(g) = -393.5 kJ/mol

(2) H2(g) + ½O2(g) H2O(l) = -285.8 kJ/mol

(3) C5H12(g) + 8O2(g) 5CO2(g) + 6H2O(l) H = -3535.6 kJ/mol


v. Sample Problem E

1. Calculate the change in enthalpy for this reaction.

2H2(g) + 2CO2(g) 2H2O(g) + 2CO(g)

State whether the reaction is exothermic or endothermic.

10.4: Order and Spontaneity

I. Entropy

a. Some reactions happen easily, but others do not.

i. Sodium and chlorine react when they are brought together.

ii. Nitrogen and oxygen coexist in the air you breathe without forming poisonous nitrogen

monoxide, NO.

b. One factor you can use to predict whether reactions will occur is enthalpy. A reaction is more

likely to occur if it is accompanied by a ____________________________ or if H is negative.

c. Another factor known as entropy can determine if a process will occur.

d. Entropy, ________, is a measure of the disorder in a system and is a thermodynamic property.


e. Entropy is not a form of energy and has the units ________________________________

f. A process is ____________________ to occur if it is accompanied by an increase in entropy.

i. S is positive.

g. Factors that affect entropy

i. Ions in a solution disperse throughout the solution.

1. This process of dispersion is called diffusion and causes the increase in entropy.

ii. Entropy also increases as ________________ become more dilute or when the pressure

of a gas is reduced.

1. In both cases, the molecules fill larger spaces and so become more disordered.

iii. Entropies also increase with _____________________, but this effect is not great unless

a phase change occurs.

iv. The entropy can change during a reaction.

v. The entropy of a system can increase when the total number of ____________________

is greater than the total number of moles of reactant.

vi. Entropy can ________________ in a system when the total number of particles in the

system increases.

vii. Entropy also increases when a reaction produces more ___________________________,

because gases are more disordered than liquids or solids.

viii. Entropy decreases as sodium chloride forms: 2 mol of sodium combine with 1 mol of

chlorine to form 2 mol of sodium chloride.

1. This decrease in entropy is because of the order present in crystalline sodium

chloride.


ix. Entropy increases when 1 mol of sodium chloride dissolves in water to form 1 mol of

aqueous sodium ions and 1 mol of aqueous chlorine ions.

1. This increase in entropy is because of the order lost when a crystalline solid

dissociates to form ions.

h. Hess’s Law also applies to entropy

i. The decomposition of nitrogen triiodide to form nitrogen and iodine creates 4 mol of gas

from 2 mol of a solid.

ii. This reaction has such a large ___________________________ that the reaction

proceeds once the reaction is initiated by a mechanical shock.

iii. Molar entropy has the same unit, J/K•mol, as molar heat capacity.

iv. Molar entropies can be calculated from _________________________________ data.

v. Entropies can also be calculated by using Hess’s law and entropy data for other reactions.

1. You can manipulate __________________________ using rules of algebra to get

a desired equation.

vi. When equations are added or subtracted, entropy changes must be added or subtracted.

vii. When equations are multiplied by a constant, the entropy changes must also be multiplied

by that constant.

viii. Atoms and molecules that appear on both sides of the equation can be _______________.


ix. The standard entropy is represented by the symbol S0.

x. The standard entropy of the substance is the entropy of ____________ of a substance at a

standard temperature, __________________.

xi. Elements can have standard entropies that have values other than zero.

xii. Most standard entropies are _________________; this is not true of standard enthalpies

of formation.

xiii. The entropy change of a reaction can be calculated by using the following equation.

xiv. Sample Problem F

1. Calculate the entropy change that accompanies the following reaction.


II. Gibbs Energy

a. The tendency for a reaction to occur depends on both H and S.

b. If H is ________________ and S is _______________ for a reaction, the reaction will

likely occur.

c. If H is positive and S is negative for a reaction, the reaction will not occur.

d. How can you predict what will happen if H and S are both positive or both negative?

e. ________________________ is the energy in a system that is available for work represented by

the symbol G.

G = H – TS

f. Another name for Gibbs energy is ____________________.

g. Gibbs Energy Determines Spontaneity!!!

i. A ________________________ reaction is one that does occur or is likely to occur

without continuous outside assistance, such as input of energy.

1. A reaction is spontaneous if the Gibbs energy change is negative.

ii. A ________________________ reaction will never occur without assistance.

1. If a reaction has a G greater than 0, the reaction is nonspontaneous.

iii. If a reaction has a G of exactly zero, the reaction

is at equilibrium.

h. Entropy and Enthalpy determine Gibbs energy

i. Reactions that have __________________________ G values often release energy and

increase disorder.


ii. The vigorous reaction of potassium metal and water is an example of this type of

reaction.

iii. The change in Gibbs energy for the reaction is

iv. You can calculate G in another way because lists of standard Gibbs energies of

formation exist.

v. The standard Gibbs energy of formation, __________, of a substance is the change in

energy that accompanies the formation of 1 mol of the substance from its elements at

298.15 K.

vi. The ___________________________________________can be used to find the G for

any reaction.

vii. Hess’s law also applies when calculating ________


viii. Sample Problem G

1. Given that the changes in enthalpy and entropy are –139 kJ and 277 J/K

respectively for the reaction given below, calculate the change in Gibbs energy.

Then, state whether the reaction is spontaneous at 25C.

ix. Sample Problem H

1. Calculate G for the following water-gas reaction.

C(s) + H2O(g) CO(g) + H2(g)

2. Is this reaction spontaneous?


x. Predicting Spontaneity

1. Does temperature affect spontaneity?

2. Consider the equation for G.

G = H - TS

3. The terms H and S change ______________________ as temperature changes.

4. The presence of T in the equation for G indicates that temperature may greatly

affect G.

5. Suppose a reaction has both a ______________ H value and a _____________

S value.

a. If the reaction occurs at a low temperature, the value for TS will be

_____________ and will have little impact on the value of G.

b. The value of G will be similar to the value of H and will have a positive

value.

6. When the same reaction proceeds at a high enough temperature, ___________

will be larger than H and G will be negative.

7. Increasing the temperature of a reaction can make a nonspontaneous reaction

spontaneous.

8. A nonspontaneous reaction cannot occur unless some _____________________

is added to the system.


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