Name: _______________________________________ Period: __________________________

Unit 12: Energy and Thermodynamics- Guided Notes

What is Energy?

_______________________________ is the ability to do work or produce heat. There are two types of energy:

o _______________________________________________- Energy of positiono _______________________________________________- Energy of motion

__________________________________________________ energy can be converted from one form to another but can be neither created nor destroyed

_________________________________________ is the science of heat, temperature, and of the laws governing the conversion of thermal energy into mechanical, electrical, or other forms of energy

What is Temperature?

Temperature is a measure of the ___________________________________________________ of a substance. The _____________________________________ the kinetic energy/faster the random motions of atoms or

molecules – the __________________________ the temperature The _____________________________________ the kinetic energy/slower the random motions of atoms or

molecules – the __________________________ the temperature

What is Heat?

Heat is the _______________________ of ____________________________ between two objects due to a temperature difference between the objects.

Heat is the way in which thermal energy is transferred from a ___________________ object to a _____________________ object.

Heat is represented by _____________ If you touched a hot stove the energy from the stove will be transferred to you hand.

o Thus it feels ______________. If you were to touch ice, the energy from your hand will be transferred to the ice.

o Thus it feels ______________.

Endothermic and Exothermic Processes

________________________________ – the object of focus ____________________________________ – everything around the system System plus surroundings equals the __________________________________________ ____________________________ – energy flows out of the system to the surroundings

o Feels ______________ ____________________________ – energy flow into the system from the surroundings

o Feels ______________ From the point of view of the ice, is the ice melting is an exothermic or endothermic process? _______________ From the point of view of the hot cup of coffee, holding the cup of coffee with you hand, is it exothermic or

endothermic? ____________________________ From the point of view of the cup, putting a cup of water in the freezer: ______________________________ From the point of view of the water, boiling water on a stove: __________________________________ Melting: ___________________ Freezing: ___________________

Energy in Reactions:1

___________________________ Energy- The minimum energy required in for a chemical reaction to occuro High activation energy slows the rate of reactiono Low activation energy speeds up the rate of reaction

Once the reactants have gained enough energy (the activation energy), they are considered to be the _____________________________________________

o The activated complex is an ______________________________ between reactants and products After the activated complex state, the ___________________________ are formed Some of these reactions are _________________________ and the graphs can be read for the reverse reaction ____________________________________: The amount of energy transferred between the system (the

reaction) and the surroundings (how much energy is gained or lost)o ΔH = _______________________________o ΔH = _____________ (endothermic)

More heat goes from ______________________ into ____________________o ΔH = ______________ (exothermic)

More heat leaves _______________________ and goes into ___________________________o Energy is not created or destroyed just transferred between system and surroundings

(_____________________________________________)o _________________________( ΔH) is equal to ___________________(q) if pressure remains constanto q = ∆H

Reaction Coordinate Diagram

For questions 1-6 use the graph to the right:

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1. What is the activation energy for this reaction? __________________________2. What is the change in enthalpy for this reaction? _________________________3. Is this an endothermic or exothermic reaction? __________________________4. If this reaction occurred in a beaker, how would the beaker feel? ____________5. What is the change in enthalpy for the reverse reaction? __________________6. What is the activation energy for the reverse reaction? ____________________

For questions 7-12 use the graph to the left:

7. What is the activation energy for this reaction? ______________________

8. What is the change in enthalpy for this reaction? ___________________

9. Is this an endothermic or exothermic reaction? ____________________

10. If this reaction occurred in a beaker, how would the beaker feel? ______

11. What is the change in enthalpy for the reverse reaction? ____________

12. What is the activation energy for the reverse reaction? ______________

Catalysts and Inhibitors

_______________________________: a substance that speeds up a reaction without being consumed (not part of the reaction)

How do catalysts work? o They ___________________________ the activation energy

(Now less energy is required for the reaction to take place)o They increase the ____________________________ of the

forward AND the reverse reaction An example of a catalyst is an _____________________________

o ____________________________: a large molecule, usually a protein, which catalyzes biological reactions (reactions in your body)

_________________________________: a substance that slows down a reaction without being consumed (not part of the reaction)

o Decreases the ___________________ of the forward AND reverse reaction Draw the effects of a catalyst on the energy diagram above:

Phase Changes

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Phase changes is dependent on the ______________________ and the _______________________.

o So if you change the _____________________ around the substance, you can change its state of matter.

o Also if you change the _______________________ of the substance, you can change its state of matter.

Another way we can look at phase changes is called a heat curve ______________________________ is a plot of temperature verses time for a substance where energy is added

at a constant rate

Slanted Lines:o _______________________ phase of matter exists o ____________________________ absorbed is used to heat up that phase of matter (solid, liquid, or gas)o ________________________________ energy is increasing (shown by an increase in

___________________________) (________________________ energy increases as well)o Formula: _________________________________

Plateaus/Flat Lines:o Signify a ___________________________________________ (two phases exist in equilibrium) o At this point, ____________________________ is being added to change phase only. o No change in ________________________ energy (no change in ____________________) only change

in __________________________________ energyo The temperature will remain at ____________________________ until all the substance changes phase. o Formulas:

Melting: _____________________________________ Boiling: _____________________________________

Energy

Different material respond to heat differently. We can measure the heat that is transferred from one substance to the next.

The units for energy ______________________ or _________________________. _____________________________ (lowercase c)– the amount of energy (heat) required to raise the

temperature of ___________________ of water by ___________________. The SI Unit of energy is ____________________.

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1 calorie = 4.184 joules 1 _____________________ = 1 food _______________________ (capital c)

Heat of Fusion and Heat of Vaporization

Latent heat of _________________ (___________________): amount of heat needed to melt 1 gram of solido Units are __________________________________

Latent heat of ________________ (___________________): amount of heat needed to vaporize 1 gram of liquido Units are ________________________________________________

To find the energy absorbed during a phase change use:o Melting: ________________________________________________o Boiling: _________________________________________________

Example #1: The latent heat of fusion of ice is 335,000 J/kg . How much energy is needed to melt 0.65 kg of ice?

Specific Heat Capacity

________________________________________________________ is the energy required to change the temperature of a mass of one gram of a substance by one Celsius degree.

o __________________ have low specific heat values, they require less energy to heat up and cool down o ___________________________________ have high specific heat values, they require more energy to

heat up and cool down

Energy

It takes energy to heat stuff up For pure substance in single phase of matter - can calculate how much E needed using: ____________________

o _____________ = heat energy in Jouleso _____________ = mass in gramso _____________ = specific heat capacity in J/g◦Co _____________ = change in temperature in ◦C (____________________________)

When something cools down, energy is _______________________, q ____________0 When something heats up, energy is _________________________, q ____________0 Example #2: Determine the amount of energy (heat) is joules required to raise the temperature of 7.40g of

water from 29.0°C to 46.0°C.

Example #3: A 1.6-g sample of a metal that has the appearance of gold requires 5.8J of energy to change its temperature (and not state of matter) from 23°C to 41°C. Is the metal pure gold?

Example #4: What is the final temperature of a 7.31 g piece of aluminum at 34.0°C if 354J of energy is applied to the aluminum? (the specific heat of Al is 0.890 J/g°C and the melting point of Al is 660°C.)

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Example #5: A 4.32g sample of copper is subjected to 458J of energy. By how much did the temperature increased (assume no phase change)?

Example #6: How much energy is required to heat a 5.80 g sample of ice at -12.0oC to 45.0oC?

Example #7: How much energy is required to heat a 6.70 kg sample of water from 25.0oC to 105.0oC?

Calorimetry

________________________ is used to measure amounts of heat transferred to or from a system.o Remember a system can be a _______________________, ________________________,

______________________, etc. A ___________________________is a device used to measure the amount of heat involved in a chemical or

physical process. The amount energy _________________________ or __________________________ by the system is the same

amount of energy gained or lost by the _________________________ inside the calorimeter qgained = - qgained OR qsystem = - qwater OR mc∆T = -mc∆T During the calorimetry experiment the

__________________________________________ of the water is measured We can calculate the change in energy for the water using

_________________________________ We can then calculate the change in energy for the system by using the

______________________________ In a simple calorimeter, the system occurs in the _______________________ The ________________________________ is used to measure the change in

temperature of the water Other calorimeters uses different methods to measure the change in energy Calorimeters are used to determine the amount of calories in

______________________ A small amount of energy is gained or lost by the actual _________________

o This is accounted for during experiments Example #1: A 1.000 g sample of octane (C8H18) is burned in a calorimeter

containing 1200 grams of water at an initial temperature of 25.00ºC. After the reaction, the final temperature of the water is 33.20ºC. The specific heat of water is 4.184 J/g ºC. Calculate the heat of combustion of octane in kJ/mol (ignore the energy gained or lost by the calorimeter).

Example #2: A 20.0 g sample of iron at a temperature of 120.0oC is placed into a container of water. There are 300 mL of water in the container at a temperature of 30.0oC. What is the final temperature of the water?

Ciron = 0.444 J/goC Cwater = 4.184 J/goC ρwater = 1 g/mL

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Enthalpy in Reactions

The change in enthalpy (_______________) is written as a part of the chemical equation OR after the balanced chemical equation

Endothermic Reactions: Enthalpy is treated as a _______________________ if part of the reaction OR enthalpy is ______________________________ value written after the reaction

o Example: When nickel (II) sulfite decomposes, it absorbs 156 kJ of energy.o 156 kJ + NiSO3 (s) NiO (s) + SO2 (g)o NiSO3 (s) NiO (s) + SO2 (g) ΔH = 156 kJ

Exothermic reactions: enthalpy is treated as a ________________________ if part of the reaction OR enthalpy is a ________________________ value written after the reaction

o Example: When sulfur and oxygen react to produce sulfur dioxide, 297 kJ of energy is releasedo S (s) + O2 (g) SO2 (g) + 297 kJo S (s) + O2 (g) SO2 (g) ΔH = -297 kJ

_________________________- states that the enthalpy of a whole reaction is equivalent to the sum of its steps. o Reactions can be ___________________________________ (reversed, added, multiplied, etc.) and their

_______________________ values are also manipulated All reactions have a ___________________ Most substances have a known ___________________ ΔH is usually measured in units of ___________________________ The change in enthalpy is caused by bonds _______________________ and ________________________ If a reaction is __________________________, the sign of ΔH value is multiplied by __________________

o For example: 2H2O(l) → 2H2(g) + O2(g) ΔH = + 967.2 kJo What about the reverse reaction? 2H2(g) + O2(g) → 2H2O(l) ΔH = _________________________

If a reaction is ____________________ by a number, the delta H is also multiplied/divided by the same number:o For example what if we tripled the amount of water?o 6H2O(l) → 6H2(g) + 3O2(g) ΔH = ____________________________________

What if we halved the reaction?o H2O(l) → H2(g) + ½ O2(g) ΔH = __________________________________

Hess’s Law allows us to __________________ chemical equations to determine potential ΔH of reactionso We can add reactants, products, and H o We can simplify, multiply by coefficients, and reverse a reaction

Tips for applying Hess’s Law:o Work backward from the required reaction, using the reactants and products to decide how to

manipulate the other given reactions at your disposal.o Reverse any reactions as needed to give the required reactants and products.o Multiply reactions to give the correct numbers of reactants and products.o Cancel out substances that are on both sides of the reaction

Example #1: When methane is burned in oxygen, carbon dioxide and water are produced.CH4 + 2 O2 CO2 + 2 H2O

Calculate the change in enthalpy when methane is burned using the following:C + 2H2 CH4 ΔH= -74.80 kJC + O2 CO2 ΔH= -393.50 kJH2 + ½ O2 H2O ΔH= -285.83 kJ

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Example #2: Methanol-powered cars are an idea for alternative fuel. What is the change in enthalpy of the reaction for methanol burning in a car? 2 CH3OH(l) + 3 O2(g) 2 CO2(g) + 4 H2O(g) ΔHrxn = ?Given the following information:2 CH4(g) + O2(g) 2 CH3OH(l) ΔHrxn = -328 kJCH4(g) + 2 O2(g) CO2(g) + 2 H2O(g) ΔHrxn = -802.5 kJ

Example #3: Given the following data: S(s) + 3/2O2(g) → SO3(g) ΔH = -395.2 kJ2SO2(g) + O2(g) → 2SO3(g) ΔH = -198.2 kJ

Calculate ΔH for the following reaction: S(s) + O2(g) → SO2(g)Given the following data: C2H2(g) + 5/2O2(g) → 2CO2(g) + H2O(l) ΔH = -1300 kJ

C(s) + O2(g) → CO2(g) ΔH = -394 kJH2(g) + 1/2O2(g) → H2O(l) ΔH = -286 kJ

Calculate ΔH for the following reaction: 2C(s) + H2(g) → C2H2(g)

Example #4: Given the following data: 2O3(g) → 3O2(g) ΔH = - 427 kJO2(g) → 2O(g) ΔH = + 495 kJNO(g) + O3(g) → NO2(g) + O2(g) ΔH = - 199 kJ

Calculate ΔH for the following reaction: NO(g) + O(g) → NO2(g)

Another way to calculate the Enthalpy of a Reaction:

ΔH = ΣΔHf (products) – ΣΔHf (reactants)

What does this mean? ΔH = (the sum of the enthalpy of formation of the products) - (the sum of the enthalpy of formation of the

reactants) Look at the coefficients in the chemical equation – you must account for all substances Use the coefficients to ______________________ Be careful adding and subtracting negative numbers Heat of formation (____________): The enthalpy change when ____________________ of a compound is

formed from the elements in their standard states

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__________= standard conditionso Gases at 1 atm pressure, All solutes at 1 M concentration, Pure solids and pure liquids

_______________ = a formation reactiono 1 mole of product formedo From the elements in their standard states (1 atm, 25°C)

For all elements in their standard states, ΔH°f = ___________________o Ex: Na, Cl2, C, Ag

What’s the formation reaction for adrenaline, C9H12NO3(s)?

Example #1: When methane is burned in oxygen, carbon dioxide and water are produced. Calculate the change in enthalpy when methane is burned using the following: CH4 + 2 O2 CO2 + 2 H2O

Example #2: Determine the enthalpy of formation of the following: CH4 + 2 O2 CO2 + 2 H2O

Example #3: Use the standard enthalpies of formation table to determine the change in enthalpy for the following: NaOH + HCl NaCl + H2O

Example #4: Use the standard enthalpies of formation table to determine the change in enthalpy for the following: 2 CO(g) + O2(g) 2 CO2(g)

Stoichiometry and Enthalpy:

If the enthalpy of a reaction is known, then it can be used as a _________________________________________ with stoichiometry (it is similar to a mole ratio)

What is the first step in a stoichiometry problem?___________________________________________________ Example #1: When 1 mole hydrogen and chlorine gas react to produce hydrochloric acid, 184.6 kJ of energy is

released. What is the change in enthalpy if 8.22 moles of hydrogen gas is reacted with excess chlorine?

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Example #2: For every 1 mole of nitrogen gas reacted with hydrogen gas to produce gaseous ammonia, 91.8 kJ of energy is released. How much energy is given off when 222.4 g of nitrogen reacts with excess hydrogen gas?

Example #3: Given the thermochemical equation 2CO2(g) → 2CO(g) + O2(g) ΔH = 566 kJ how much energy is absorbed when 85.2 g of CO2 are reacted?

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