Chapter 16 Energy and Chemical Change16.1 Energy

Review Vocabularytemperature: a measure of the average kinetic energy of the particles in a sample of matter

Main Idea - Energy can change form and flow, but it is always conserved.

The Nature of Energy• _________________ is the ability to do work or produce heat.

• Two forms of energy exist, ________________________________________.

• Potential energy is due to ______________________________________.

• Kinetic energy is ______________________________________.

• The __________________________________________________________states that in any chemical reaction or physical process, energy can be converted from one form to another, but it is neither created nor destroyed—also known as the first law of thermodynamics.

Tracing Energy Through a System

Example - Flashlight Example - Microphone and Speakers

New Vocabularyenergylaw of conservation of energychemical potential energyspecific heat

heatcaloriejoule

The Nature of Energy (cont.)

• _____________________________________________is energy stored in a substance because of its composition.

• Chemical potential energy is important in chemical reactions.

• ___________________ is energy that is in the process of flowing from a warmer object to a cooler object.

• ____ is used to symbolize heat.

Heat Energy Flow Example

Measuring Heat• A ___________________is defined as the

amount of energy required to raise the temperature

of one gram of water one degree Celsius.

• Food is measured in Calories,

or ___________calories (kilocalorie).

• A _______________ is the SI unit of heat and energy,

equivalent to 0.2390 calories.

Specific Heat

• The specific heat of any substance

is the amount of heat required to _________

_____________________________________.

• Some objects require more heat than others

to raise their temperature.

Calculating heat absorbed and released

q = ________________________________

c = ________________________________

m = ________________________________

ΔT = ________________________________

16.2 HeatReview Vocabulary Pressure

Main Idea - The enthalpy change for a reaction is the enthalpy of the products minus the enthalpy of the reactants.

Chemical Energy and the Universe• Virtually every chemical reaction is accompanied by absorption or release of energy.

• Energy is ________________________to break bonds of reactants and energy is ________________________ when bonds form.

• _____________________________ is the study of heat changes that accompany chemical reactions and phase changes.

• The ____________________is the specific part of the universe that contains the reaction or process you wish to study.

• The _________________________ are everything else other than the system in the universe.

• The__________________________ is defined as the system plus the surroundings.

Calorimetry• A _____________________________ is an insulated device used for measuring the amount of

heat absorbed or released in a chemical reaction or physical process.

New Vocabularycalorimeterthermochemistrysystemsurroundings

universeenthalpyenthalpy (heat) of reaction

Chemists are interested in _____________________________________ during reactions.

• ____________________ is the heat content of a system at constant pressure.

• _________________________________ is the change in enthalpy during a reaction symbolized as ΔHrxn.

Enthalpy changes for exothermic reactions are always negative.

• Enthalpy changes for endothermic reactions are always positive.

13.4 Phase ChangesReview Vocabulary phase change

Main Idea - Matter changes phase when energy is added or removed.

Phase Changes That Require Energy• Heat is the transfer of energy from an object at a higher temperature to an object at a lower

temperature.

• Melting occurs when heat flows into a solid object.

• When ice is heated, the ice eventually absorbs enough energy to break the hydrogen bonds that hold the water molecules together.

• When the bonds break, the particles move apart and ice melts into water.

• The melting point of a crystalline solid is the temperature at which the forces holding the crystal lattice together are broken and it becomes a liquid.

• Particles with enough energy escape from the liquid and enter the gas phase.

• Vaporization is the process by which a liquid changes to a gas or vapor.

• Evaporation is vaporization only at the surface of a liquid.

• In a closed container, the pressure exerted by a vapor over a liquid is called vapor pressure.

• The boiling point is the temperature at which the vapor pressure of a liquid equals theatmospheric pressure.

• Sublimation is the process by which a solid changes into a gas without becoming a liquid.

New Vocabularymelting pointvaporizationevaporationvapor pressureboiling point

freezing pointcondensationdepositionphase diagramtriple point

Phase Changes That Release Energy• As heat flows from water to the surroundings, the particles lose energy.

• The freezing point is the temperature at which a liquid is converted into a crystalline solid.

• As energy flows from water vapor, the velocity decreases.

• The process by which a gas or vapor becomes a liquid is called condensation.

• Deposition is the process by which a gas or vapor changes directly to a solid, and is the reverse of sublimation.

Phase Diagrams• A phase diagram is a graph of pressure versus temperature that shows in which phase a

substance will exist under different conditions of temperature and pressure.

• The triple point is the point on a phase diagram that represents the temperature and pressure at which all three phases of a substance can coexist.

• The phase diagram for different substances are different from water.

16.3 Thermochemical EquationsReview Vocabulary combustion reaction: a chemical reaction that occurs when a substance reacts with oxygen, releasing energy in the form of heat and light

Main Idea - Thermochemical equations express the amount of heat released or absorbed by chemical reactions.

Writing Thermochemical Equations• A thermochemical equation is a balanced chemical equation that includes the physical states of

all reactants and products, and energy change.

• The enthalpy (heat) of combustion of a substance is the enthalpy change for the complete burning of one mole of the substance.

• Molar enthalpy (heat) of vaporization refers to the heat required to vaporize one mole of a liquid substance.

• Molar enthalpy (heat) of fusion is the amount of heat required to melt one mole of a solid substance.

Combustion Reactions• Combustion is the reaction of a fuel with oxygen.

• Food is the fuel in combustion reactions in biological systems.

New Vocabularythermochemical equationenthalpy (heat) of combustionmolar enthalpy (heat) of vaporizationmolar enthalpy (heat) of fusion

Examples

16.4 Thermochemical Equations

Main Idea - The enthalpy change for a reaction can be calculated using Hess’s law.

Hess’s Law• Hess’s law states that if you can add two or more thermochemical equations to produce a final

equation for a reaction, then the sum of the enthalpy changes for the individual reactions is the enthalpy change for the final reaction.

• The standard enthalpy (heat) of formation is defined as the change in enthalpy that accompanies the formation of one mole of the compound in its standard state from its elements in their standard states.

• Elements in their standard states have a ________________________________.

• The formation of compounds are placed above or below elements in their standard states.

• Standard enthalpies of formation can be used to calculate the enthalpies for many reactions under standard conditions by using Hess’s law.

• The summation equation

New VocabularyHess’s lawstandar enthalpy (heat) of formation

16.5 Reaction Spontaneity

Main Idea - Changes in enthalpy and entropy determine whether a process is spontaneous.

Spontaneous Processes• A spontaneous process is a physical or chemical change that once begun, occurs with no outside

intervention.

• Many spontaneous processes ______________________________ from the surroundings to start the process.

• __________________ is a measure of the possible ways that the energy of a system can be distributed, and this is related to the freedom of the system’s particles to move and the number of ways they can be arranged.

• The second law of thermodynamics states that spontaneous processes always proceed in such a way that the ___________________________________________.

• Entropy is sometimes considered a measure of ________________________________ of the particles in a system.

• The more __________________________ the particles are, the more ______________.

• Entropy changes associated with changes in state can be predicted.

• Entropy _________________ as a substance changes from a solid to a liquid and from a liquid to a gas.

• Dissolving a gas in a solvent always results in a __________________ in entropy.

• Assuming no change in physical state occurs, the entropy of a system usually increases when the number of gaseous product particles is greater than the number of gaseous reactant particles.

• With some exceptions, entropy increases when a solid or liquid dissolves in a solvent.

New Vocabularyspontaneous processentropysecond law of thermodynamicsfree energy

• The _______________________ of particles of a substance __________________as its temperature increases.

Entropy, the Universe, and Free Energy• In nature, the change in entropy tends to be positive when:

o The reaction or process is exothermic, which raises the temperature of the surroundings

o The entropy of the system increases.

• Free energy is energy that is available to do work.

o Gibbs free energy equation

__________________________________

If the sign of the energy change, ΔG°, is_________________, the reaction is

________________________

If the sign of the energy change is ________________, the reaction is s___________________________.

• The entropy of the universe (system + surroundings) __________________________ in any spontaneous process.