Thermochemistry & States of MatterUnit 10 Section 1 Obj. 3Energy in Chemical & Physical ProcessesThermochemistry

Study of changes that accompany chemical reactions and phase changes The Universe is considered to be made of 2 parts:

1. System: part that contains the reaction or process2. Surroundings: everything else

Energy Energy is defined as the ability to do _____________________ or transfer __________________

energy. There are 2 forms of energy. Chemical systems contain both Potential Energy and Kinetic

Energy.

1. Potential Energy (PE): Energy at rest due to the _________________ of an object; chemical potential energy is the energy stored in a substance’s _________________________.

2. Kinetic energy (KE): Energy of the _______________ of particles in a substance and is _____________________ proportional to KELVIN temperature. As temperature increases, KE also ___________________.

Example: 100 K 200 K KE will ___________________

BUT 25°C 50 °C KE increases by a factor of 1.08

Law of Conservation of Energy states that energy is neither _________________ nor destroyed, just changed in form

C8H18 + O2 H2O + CO2 + EnergyStored PE converts to 25% work and 75% heat

Energy in chemical Reactions

Enthalpy (H) : heat released or absorbed during a chemical reaction; classified as positive or negative

HOT PACK An exothermic reaction is when the system ___________________ energy; heat flows

___________ of the reaction and the surroundings get ________________. They have a ____________________ H

H products < H reactants

4Fe + 3 O2 2 Fe2O3 + 1625 kJ or 4Fe + 3 O2 2 Fe2O3 H = - 1625 kJ

COLD PACK An endothermic reaction is when the system ___________________ energy; heat flows

___________ a reaction and the surroundings get ___________________. They have a ____________________ H

H products > Hreactants

27kJ + NH4NO3(s) NH4(aq)+1+NO3(aq)

-1 or NH4NO3(s) NH4(aq)+1

+ NO3(aq)-1H = +

27 kJ

To calculate Ea: Subtract the energy of reactants from the energy of the activated complex

Ea = Etransition state - Ereactant

Heat of Reaction (H): Heat of the reaction; can be1. Endothermic: (H is positive); products have higher energy than the reactants2. Exothermic: (H is negative); products have lower energy than the reactants

To calculate: Subtract the energy of the reactants from the energy of the products

Hrxn = Hproducts - Hreactants

What is the difference between “Heat” and “Temperature”?

Temperature HeatInstrument

used to measure this

Unit used to measure this

Definition

A measure of the average ________________________

of the molecules in a substance.

A measure of the________________ of the molecules.

A measure of how or cold something is.

The total amount of energy in a substance. A form of

___________ that is transferred between objects because one is warmer than

the other.

It depends on 3 things: 1. __________________2. ___________________3.____________________

Units of Heat Energy

A calorie is defined as the amount of heat needed to raise the temperature of 1 g of water by 1 C

1 cal= 4.184 J Food “Calories” are kilocalories. 1 kcal = _________ calories.

Unit 10 Section 2 Obj. 2Calculating HeatSpecific Heat Amount of heat required to raise the ______________________________ of 1 g of a

substance by 1 C Different substances have different specific heats. Water has a specific heat of ____________________. Iron (Fe) has a specific heat of .449

J/gC. Gold (Au) has a specific heat of .129 J/gC. The higher the ________________________ the more energy it takes to change its

temperature.

Calculating Heat

Example: A 155 g sample of an unknown substance was heated from 25.0 C to 40.0 C. The substance absorbed 5696 J of energy. What is the specific heat?

q = m x c x T

Example: How much heat is needed to change the temperature of 12.0 g of silver with a specific heat of 0.057 cal/g°C from 25.0°C to 83.0 °C?

Unit 10 Section 3 ExtensionCalorimetry: Measuring Heat (q)A coffee cup calorimeter measures heat at constant pressure; works on the premise that the amount of heat ___________________ in a reaction or physical change is equal to the amount of heat __________________ by the water - q = + q Rearrange the specific heat equation: q = m x c x ∆T

Example: Let’s Draw it out!A piece of unknown metal with mass 17.19 g is heated to an initial temperature of 92.50 °C and dropped into 25.00 g of water (with an initial temperature of 24.50 °C) in a calorimeter. The final temperature of the system is 30.05°C. What is the specific heat of the metal? Specific heat of water = 4.184 J/g° C

Example:A 32.07 gram sample of vanadium was heated to 75.00 °C (its initial temperature). It was then dumped into a calorimeter. The initial temperature of the calorimeter’s water was 22.50 °C. After the metal was allowed to release all its heat to the calorimeter’s water, 26.30 °C was the final temperature. What mass of distilled water was in the calorimeter?

Specific heat of vanadium = .4886 J/gC Specific heat of water = 4.184 J/gC

Unit 10 Section 4 Obj. 1States of Matter

Properties Solid Liquid Gas

Packing:closeness of

particles

Attractive Forces

between particles

Movement

Vibrate in placeCan’t switch

placesLow _____________ of

particles

Rapid Random chaotic motion

High ___________ of particles

Shape

Volume:how much space is taken up

Compressibilityability for

particles to move closer

together

Changes in State

Endothermic physical changes of stateo Kinetic Energy must be put INTO the substance in order to increase the

____________________of the molecules so as to break the ___________________________ forces holding the particles together

Melting: change of state from a solid to a ________________________

Vaporization (Boiling or Evaporation): change of state from a ________________________ to a gas

Sublimation: direct change of state from a __________________________ to a gas

Exothermic physical changes of stateo Kinetic Energy must be taken OUT (removed) the substance in order for the

molecules to _____________ down so that the ___________________________ forces can begin to hold the particles together

Freezing: change of state from a _____________________ to a solid Condensation: change of state from a gas to a ____________________ Deposition: direct change of state from a __________________ to a solid

Temperature of State Changes

Freezing point (fp) is the temperature at which the liquid turns into a solid Melting point (mp) is the temperature at which the solid turns into a liquid Freezing Point = Melting Point

Example: Water has a mp and a fp of 0 C

Boiling point (bp) is the temperature at which the liquid turns into a gas Condensation point (cp) is the temperature at which a gas turns into a liquid Boiling Point = Condensation Point

Example: Water has a bp and a cp of 100 C

****All substances have their own specific freezing and boiling point which makes this physical property a great way to identify an unknown substance.

****

Unit 10 Section 5 ExtensionAtmospheric Pressure vs Vapor Pressure

Pressure Atmospheric Pressure Vapor Pressure

Force per unit area created as gas molecules collide

with objects

force per unit area exerted against a surface by the

weight of the air molecules above the surface

Force per unit area of the gas molecules above a

liquid colliding

Usually measured in newtons/meter 2 but in

chemistry we use atmospheres (atm) or millimeters of mercury

( ______________)

The more air molecules above a surface, the more molecules to exert a force

and thus a ______________________ air

pressure

The ____________________ the attractive forces, the higher the vapor pressure

At sea level, atmospheric pressure equals ________

atm or 760 mm Hg

Substances with high vapor pressure are called __________________

There are only 2 factors that control VAPOR PRESSURE!

1. Temperature2. Attractive forces of the liquid

When the vapor pressure of a liquid = atmospheric pressure, boiling will occur. Normal boiling point is @ 760 mmHg

Vaporization: Difference between Evaporation and Boiling

Evaporation occurs spontaneously at all temperatures at the ______________________________ of the liquid

Boiling occurs when extra _________________________________ known as heat is added and takes places within the body of the liquid

Boiling occurs at only 1 temperature dependent on pressure

Another definition of Boiling Point

When external atmospheric pressure = vapor pressure of a liquid

At 90C, the water’s vapor pressure is not strong enough to push against the atmospheric pressure starting to boil

At 100C, the water’s vapor pressure is equal to the atmospheric pressure boiling is

occurring

Since atmospheric pressure changes at various altitudes, we use “____________________” boiling point to describe the temp at which a LG at 1 atm

Important Ideas

The higher in altitude the _________________________ the atmospheric pressure At higher altitudes, the boiling point is ______________________________ It takes _______________________________ to cook foods at higher altitudes (lower

atmospheric pressures)

Unit 10 Section 6 Section 1

Heating & Cooling Curves

A diagram that shows how solids, liquids & gases change state when ______________________________ is changed

Plateaus = the changes of state (freezing, melting, etc.) Freezing Point & Melting Point are at the temperature or at the same plateau Boiling Point &Condensation Point are at the same temperature or at the same

plateau Slopes= pure states (solid, liquid or gas) At the plateaus, ______________________ energy remains constant because

temperature remains constant while potential energy changes At the slopes, kinetic energy _______________________________ because temperature

changes while potential energy remains constant

**DANGER!!** Notice that a gas can get higher than boiling point!

SELF CHECK: Heating Curve

1. What is the boiling point of the substance? 2. What letter represents the solid state only? 3. What letter represents the melting process?SELF CHECK: Cooling Curve

1. While the substance is cooling during the liquid phase, the average kinetic energy of the molecules of the substance will: Increase Decrease Stay the Same

2. What is the freezing point of this substance?

3. How long does it take for the gas to completely liquefy

Phase Diagram

A diagram that shows how solids, liquids & gases change state as both temperature and ____________________________ are changed

Crossing a line between states determines the change of state (boiling, melting, etc) A point directly on a line will identify the pressure and temperature (boiling point,

melting point, etc.) of the phase change _______________________________is the temperature and pressure in which all 3 of the

states coexist ______________________________is the temperature & pressure at which a gas can no

longer liquefyImportant information regarding the Phase Diagram of Water:

Comparing the Phase Diagrams of Water and Carbon Dioxide

Slope of the solid/liquid line is negative in water and positive in carbon dioxide

SELF CHECK: See diagram

[1]What is the temperature (freezing point) of line B at 1 atm?

[2]What is the temperature (boiling point) of line Cat 1 atm?

[3]What is point D?[4]What is point E?

[5]What change of state happens when you cross line B at a constant pressure of 10 atm and increase temperature?

[6]What change of state occurs when you cross line A at constant pressure of .001 atm?

[7]What change of state happens when you cross line C at 400 K to 300 k at approximately 5 atm?

Unit 10 Section 7 Obj. 2 cont.Measuring Heat during Phase Changes

Heat of Fusion/Solidification

Latent Heat of fusion (Hfus ) is the heat energy required to melt one gram of a solid at its melting point

q = Hfus x mass For water, Hfus = 334 J/g On reference sheet

Latent Heat of solidification (Hsolid ) is the heat energy lost when one gram of a liquid freezes to a solid at its freezing point

q = Hsolid x mass For water, Hsolid = -334 J/g

Heat of Vaporization/Condensation Latent Heat of vaporization (Hvap) is the heat to vaporize one gram of a liquid at its

normal boiling pointq = Hvap x mass

For water, Hvap= 2260 J/g On reference sheet

Latent Heat of condensation (Hcond ) is the heat energy released when one gram of a liquid forms from its vapor

For water, Hcond = -2260 J/gq = Hcond x mass

Examples1. How much heat is needed to melt 500.0 g of ice at 0 C?

2. How much heat is evolved when 1255 g of water condenses to a liquid at 100°C?

3. How much heat is evolved when 50.0 g of ice changes from -30.0 °C to a gas at 110°C?This is a multi step problem.