E1Q1 - 5.1-5.9; 17.1-17.4
Fuel Density
Quantity of energy released during the complete combustion of 1 liter of a liquid fuel (just multiply the fuel value by their densities to get kJ/L)
Thermodynamics
Study of energy and its transformations from one form to another
Thermochemistry
Study of the relation between chemical reactions and changes in energy
Open System
System that exchanges both energy and matter with the surroundings
Closed System
System that exchanges energy, but not matter, with the surroundings
Isolated System
System that exchanges neither energy nor matter with the surroundings
calorie (cal)
The amount of energy needed to raise the temperature of 1 g of water by 1°C, from 14.5°C to 15.5°C
Energy
The capacity to do work or produce heat
Electrostatic Potential Energy (define & equation)
The energy a particle has because of its electrostatic charge and its position with respect to another particle ***IMPORTANT NOTE*** The formula is just like the picture, but withOUT the k
First Law of Thermodynamics (define & equation)
The energy of the universe is constant (aka another way to say the law of conservation of energy) ΔE system + ΔE surroundings = 0
Heat
The energy transferred between objects because of a difference in their temperatures
Enthalpy Change
The heat absorbed by an endothermic process or given off by an exothermic process occurring at constant pressure
Calorimeter Constant (define & equation)
The heat capacity of a calorimeter C calorimeter = q calorimeter / ΔT
Thermal Energy
The kinetic energy of atoms, ions, and molecules
A chemical cold pack contains a small pouch of water inside a bag of solid ammonium nitrate. To activate the pack, you press on it to rupture the pouch, allowing the ammonium nitrate to dissolve in the water. The result is a cold, aqueous solution of ammonium nitrate. If we define the system as the NH4NO3 and the surroundings as the water, what are the signs of ΔHsystem and qsurroundings?
The low temperature of the cold pack (the system) means that heat flows into it from its warmer surroundings, so the sign of ΔH of the system is positive and the sign of the q surroundings is negative
Standard State
The most stable physical state of a substance (solid, liquid, or gas) under standard conditions
System
The part of the universe that we are studying
Heat Capacity
The quantity of energy needed to raise the temperature of an object by 1°C at constant pressure
Internal Energy (define & equation)
The sum of all of the kinetic and potential energies (aka the total energy) of all of the components of a system ΔE = q + w
T or F Energy can be thought of as a reactant for an endothermic reaction.
True
T or F In a constant pressure process, the heat equals the ΔH.
True
T or F Paired phase changes (i.e. freezing and melting, vaporization and condensation, and sublimation and deposition), have equal and opposite ΔH / q values.
True
T or F When all the coefficients are multiplied by a number, the change in enthalpy is multiplied by the same number.
True
T or F ΔH and ΔE have very similar values when there is no change in volume.
True - Thus, they have different values when there IS a change in volume
What is the enthalpy equation at constant pressure?
When at constant pressure, PV = 0 ΔH = q sub p
What is the equation for change in energy when a reaction is done at a constant volume?
When volume is constant, then ΔV = 0 ΔE = q - PΔV ΔE = q sub v
Which of the following reactions are formation reactions at 25°C? Explain why or why not. a - H2(g) + 1/2O2(g) --> H2O(g) b - C(s, graphite) + 2H2(g) + 1/2O2 --> CH3OH(l) (CH3OH is methanol, a liquid in its standard state) c - CH4(g) + 2O2(g) --> CO2(g) + 2H2O(l) d - P4(s) + 2O2(g) + 6Cl2(g) --> 4POCl3(l) (In their standard states, P4 is a solid, Cl2 is a gas, and POCl3 is a liquid)
a) IS a formation reaction for H2O(g) because it shows 1 mole of water vapor formed and its constituent elements are in their standard states b) IS a formation reaction because it shows the product as 1 mole and is formed from its constituent elements in their standard states c) NOT a formation reaction because the reactants are not elements in their standard states and because more than 1 product is formed d) NOT a formation reaction (even though the reactants are elements in their standard states) because it produces more than 1 mole of product
The energy released by a reaction is __________ by the solution.
absorbed
For a particular process, q = -10 kJ and w = 25 kJ. Which of the following statements is true? a - Heat flows from the surroundings to the system b - The surroundings do work on the system c - ΔE = -35 kJ
b - The surroundings do work on the system
A reaction was run in a bomb (constant volume) calorimeter. This reaction produced 25.4 kJ of energy that was absorbed by the calorimeter. This reaction caused the calorimeter to heat up by 2.25°C. What is the heat capacity of the calorimeter?
c = q / ΔT = 25.4 kJ / 2.25°C = 11.3 kJ / °C
Constant pressure calorimetry can be performed in the lab with a(n) __________ calorimeter.
coffee cup
Which of the following statements is true? a - In exothermic reactions, the reactants are lower in potential energy than the products b - A chemist takes the surroundings point of view when determining the sign of work or heat c - Heat of reaction and change in enthalpy can always be used interchangeably d - Enthalpy is a state function
d - Enthalpy is a state function
When work is done by a system on its surroundings, the internal energy of the system __________.
decreases
A process in which energy flows from the system to the surroundings is called __________.
exothermic
the heat and temperature change of calorimetry are related by the __________.
heat capacity
Heat Capacity Equation
q = heat (J) ΔT = change in temperature (°C)
q calorimeter equations (x3)
q calorimeter = -ΔEcombustion q calorimeter = -ΔHcombustion q calorimeter = -ΔHreaction
Heavier particles move __________ than lighter particles with the same kinetic energy.
slower
Potential energy is an example of a(n) __________, which means it is independent of the path followed to acquire the potential energy, and only the position is important in considering potential energy.
state function
Work Equation
w = -PΔV
A tank of compressed helium is used to inflate balloons for sale at a carnival on a day when the atmospheric pressure is 0.99 atm. If each balloon is inflated from an initial volume of 0.0 L to a final volume of 4.8 L, how much P-V work, in joules, is done on the surrounding atmosphere by 100 balloons when they are inflated? The atmospheric pressure remains constant during the filling process. 1 L ⋅ atm = 101.32 J.
ΔE = q + w ΔE = q - PΔV w = -PΔV ΔV = 100 balloons ( 4.8 L / balloon) ΔV = 4.8 x 10² L w = -PΔV w = -0.99 x 4.8 x 10² L w = -4.8 x 10² L ⋅ atm w = -4.8 x 10² L ⋅ atm ( 101.32 J / L ⋅ atm ) w = -4.9 x 10^4 J = -49 kJ
Suppose we have a simplified version of a piston and cylinder in an engine. The combustion of fuel injected into the cylinder produces 155 J of energy. The hot gases in the cylinder expand, pushing the piston down and doing 93 J of P-V work on the piston. If the system is the gases in the cylinder, what is the change in internal energy of the system?
ΔE = q - PΔV ΔE = 155 J - 93 J ΔE = 62 J
The enthalpy change of a phase transition is called __________.
ΔH sub transition
What is the ΔH°f assumed to be when a substance is in its standard state?
ΔH°f = 0
Formula for calculating the standard enthalpy / heat of reaction.
ΔH°rxn = (Σnproducts)(ΔH°fproducts) - (Σnreactants)(ΔH°freactants)
The standard enthalpy of formation of NH3 (g) and HF (g) are -46 and -271 kJ, respectively. Calculate the standard enthalpy of formation for ClF3 (g) based on the following reaction. 2ClF3 (g) + 2NH3(g) --> N2(g) + 6HF(g) + Cl2(g) ΔH° = -1196 kJ
- -1196 = (6) (-271) - [ (2) (x) + (2) (-46) ] - -196 = -1626 - (2x - 92) - -(2x - 92) = 430 - 2x - 92 = -430 - 2x = -338 = x = -169 kJ/mol
How much energy would we get from burning 2.24 g of glucose when the ΔH of the combustion reaction is -2803 kJ?
- 2.24 g C6H12O6 ( mol / 180.16 g ) ( 2803 kJ / mol ) = 34.9 kJ
Calculate the amount of energy required to convert 237 g of solid ice at 0.0°C to hot water at 80.0°C. The molar enthalpy of fusion (ΔH fus) of ice is 6.01 kJ/mol. The molar heat capacity of liquid water is 75.3 J/mol⋅°C.
- 237 g ( mol / 18.02 g ) = 13.2 mol H2O - q1 = nΔHfus - q1 = ( 13.2 mol ) ( 6.01 kJ / mol ) = q1 = 79.3 kJ - q2 = ncsubpΔT - q2 = ( 13.2 mol ) ( 75.3 J / mol⋅°C ) ( 80°C ) = 79517 J = q2 = 79.5 kJ - 79.3 kJ + 79.5 kJ = 158.8 kJ
Dissolving 80.0 g of NH4NO3 in 505 g of water in a coffee cup calorimeter causes the temperature of the water to decrease by 13.3°C. What is the enthalpy change that accompanies the dissolution process, ΔHsolution, expressed in kJ/mol?
- 505 g H2O ( mol / 18.02 g ) = 28.0 mol H2O - water = surroundings and NH4NO3 = system - qsurr = ncsubpΔT - qsurr = ( 28.0 mol ) ( 75.3 J/molH2O⋅°C ) ( -13.3°C ) = qsurr = -2.81 x 10^4 J - qsys = -qsurr -qsys = -(-2.81 x 10^4 J) - qsys = 2.81 x 10^4 J - 80.0 g NH4NO3 ( mol / 80.05 g ) = 0.999 mol NH4NO3 - ΔH = kJ/mol - ΔH = ( 2.81 x 10^4 J ) / ( 0.999 mol NH4NO3 ) - ΔH = 2.81 x 10^4 J/molNH4NO3 = ΔH = 2.81 kJ/molNH4NO3
What is the calorimeter constant of a bomb calorimeter if burning 1.000 g of benzoic acid in it causes the temperature of the calorimeter to rise by 7.248°C? The enthalpy of combustion of benzoic acid is ΔHcomb = -26.38 kJ/g.
- C calorimeter = q calorimeter / ΔT - q calorimeter = -ΔHrxn - C calorimeter = (26.38 kJ/g) / (7.248°C) = 3.640 kJ/°C
Calculate the ΔH°rxn for the combustion of the fuel propane (C3H8) in air. ΔH°f CO2 = -393.5 kJ/mol ΔH°f H2O = -285.8 kJ/mol ΔH°f C3H8 = -103.8 kJ/mol ΔH°f O2 = 0 kJ/mol
- C3H8(g) + 5O2(g) --> 3CO2(g) + 4H2O(l) - ΔH°rxn = [ (3 mol CO2) (-393.5 kJ/mol) + (4 mol H2O) (-285.8 kJ/mol) ] - [ (1 mol C3H8) (-103.8 kJ/mol) + (5 mol O2) (0 kJ/mol) ] = ΔH°rxn = -2219.9 kJ/mol
The complete combustion of 0.5763 g of glucose (C6H12O6) in a calorimeter (Ccalorimeter = 6.20 kJ/°C) raises the temperature of the calorimeter by 1.45°C. What is the food value of glucose in Calories per gram?
- Ccalorimeter = q / ΔT - 6.20 kJ = q / 1.45 °C - q = 8.99 kJ - (8.99 kJ / 0.5763 g) (Cal / 4.184 kJ) = food value = 3.73 Cal / g
In a coffee-cup calorimeter, 100.0 mL of 1.0 M NaOH and 100.0 mL of 1.0 M HCl are mixed. Both solutions were originally at 24.6°C. After the reaction, the final temperature is 31.3°C. Assume that all the solutions have a density of 1.00 g/mL and a specific heat capacity of 4.18 J/K⋅g. Calculate the enthalpy change per mole for the neutralization of HCl by NaOH.
- Since the temperature of the reaction is increased, the reaction is exothermic - ΔH = q = smΔT - 100.0 mL + 100.0 mL = 200.0 mL - m = (200.0 mL ) ( 1.0 g / mL ) = m = 200.0g - 31.3°C - 24.6°C = 6.7°C - ΔH = ( 4.184 J/K⋅g ) ( 200.0 g ) ( 6.7°C ) - ΔH = 5607 J - ΔH = -5607 J (negative because it is exothermic) - 0.1000 L ( 1.0 mol H+ / L ) = 0.10 mol H+ - ΔH/mol = -5607 J / 0.10 mol = ΔH/mol = -56070 J/mol =ΔH = -56 kJ/mol
A blacksmith drops a 1.50 kg piece of iron heated to 525°C into 2.00 kg of water at 15.0°C. Given the molar heat capacity of iron as 25.1 J/mol⋅°C and the molar heat capacity of water at 75.3 J/mol⋅°C, calculate the final temperature of the water.
- q = -q - ncsubpΔT = -ncsubpΔT - ncsubp(Tfinal-Tinitial) = -ncsubp(Tfinal-Tinitial) - 1.5 kg Fe ( 1000 g / kg ) ( mol / 55.85 g ) = 26.9 mol Fe - 2.00 kg H2O ( 1000 g / kg) ( mol / 18.02 g ) = 111 mol H2O ( 26.9 mol Fe ) ( 25.1 J/molFe⋅°C ) ( Tfinal - 525°C ) = ( -111 mol H2O ) ( 75.3 J/molH2O⋅°C ) ( Tfinal - 15.0°C ) = Tfinal = 53.1°C
It takes 585 J of energy to raise the temperature of 125.6 g of mercury from 20.0°C to 53.5°C. Calculate the specific heat capacity and the molar heat capacity of mercury.
- q = msΔT - 585 J = ( 125.6 g ) s ( 33.5°C ) = s = 0.139 J/g⋅°C - c = ( 0.139 J/g⋅°C ) ( 200.59 g / mol ) = c = 27.9 J/mol⋅°C
As a system increases in volume, it absorbs 52.5 J of energy int he form of heat from the surroundings. The piston is working against a pressure of 0.500 atm. The final volume of the system is 58.0 L. What was the initial volume of the system if the internal energy of the system decreased by 102.5 J? Use the fact that 1 L⋅atm = 101.3 J.
- ΔE = -102.5 J (negative because the energy decreased) - q = +52.5 J (positive because the energy was absorbed) - ΔE = q + w - ΔE = q - PΔV - ΔE = q - P (vfinal - vinitial) - P (vfinal - vinitial) + ΔE = q - P (vfinal - vinitial) = q - ΔE - P (vfinal - vinitial) = 52.5 J - -102.5 J - P (vfinal - vinitial) = 155 J - 155 J (L⋅atm / 101.3 J) = 1.53 L⋅atm - 0.5 atm ( 58.0 L - vinitial) = 1.53 L⋅atm - 58.0 L - vinitial = 3.06 L - -vinitial = -54.9 L = vinitial = 54.9 L
Calculate the work for the expansion of an ideal gas from 2.0 L to 5.0 L against a pressure of 2.0 atm at constant temperature.
- ΔE = q - PΔV - 1 = q - (2) (5.0 L - 2.0 L) = q = -6.0 L⋅atm
Work
-A form of energy -The energy required to move an object through a given distance
State Function w/ Examples
-A property of the system that depends only on its present state -A change in a state function depends only on the initial and final states, not the path taken EXAMPLES: -Volume -Potential Energy -Temperature -Pressure -Number of Moles -Density -Enthalpy -Internal Energy
Path Function w/ Examples
-A quantity which depends on the path taken to change a system from an initial to a final state EXAMPLES: -Work -Heat
P-V Work (define & equation)
-Also called pressure-volume work -The work associated with the expansion or compression of a gas ΔE = q - PΔV
What are the 2 rules to using Hess's Law correctly?
-Cancel like terms ONLY if they appear on both sides of the equation -Add like terms ONLY if they appear on the same side of the equation
Saturated Hydrocarbons w/ Example
-Compounds containing the max ratio of hydrogen atoms to carbon atoms -Ex: Alkanes
What are the 2 ways in which energy is converted from 1 form to another?
-Heat -Work
What are the 2 ways in which energy is converted from one form to another?
-Heat -Work
Name, give the abbreviation for, and define the only 2 ways to convert one type of energy into another.
-Heat = q = Energy transfer due to temperature difference -Work = w = Force acting over a distance
List the 2 rules for enthalpies when manipulating equations.
-If a reaction is reversed, the sign of ΔH must also be reversed -If the coefficients in a balanced reaction are multiplied by an integer, the value of ΔH also must be multiplied by that same integer
Name and give the formula of all of the alkanes, in order based on their prefixes.
-METHane: CH4 -ETHane: CH3CH3 -PROPane: CH3CH2CH3 -BUTane: CH3(CH2)2CH3 -PENTane: CH3(CH2)3CH3 -HEXane: CH3(CH2)4CH3 -HEPTane: CH3(CH2)5CH3 -OCTane: CH3(CH2)6CH3 -NONane: CH3(CH2)7CH3 -DECane: CH3(CH2)8CH3
What are the 2 ways that you can manipulate equations using Hess's Law?
-Multiply the entire equation and the ΔH by a coefficient -Reverse the equation (make the reactants the products and the products the reactants, and change the sign +/- on the ΔH)
Write the following reaction showing the 86 kJ as either a reactant or product, and state whether the reactants or products are higher in energy. N2 + 2O2 --> 2NO2
-N2 + O2 + 68 kJ --> 2NO2 - Products are higher in energy
Energy is usually classified into what 2 categories?
-Potential -Kinetic
Standard Conditions
-Pressure = 1 bar = 1 atm -Temperature = Assumed to be 25°C unless otherwise specified -Concentration = 1 M
Food Value
-Quantity of energy produced when a material consumed by an organism for sustenance is burned completely -Typically reported as Calories (kilocalories) per gram of food
Enthalpy of Reaction
-The energy absorbed or given off by a chemical reaction under conditions of constant pressure -Also called heat of reaction
Kinetic Energy (define & equation)
-The energy of an object in motion -Energy of motoin
Potential Energy (define & equation)
-The energy stored in an object because of its position -Energy of position
What are the rules for writing formation reactions?
-The products must have a coefficient of 1 -We CAN use fractional exponents in the final form of the equation so ensure that the products have a coefficient of 1 -Reactants and products must be in their standard state of matter
Molar Heat Capacity (symbol, define, & equation)
-c sub p -Quantity of energy required to raise the temperature of 1 mole of a substance by 1°C ***IMPORTANT NOTE*** The formula is just like the picture, but the subscript is a p instead of an m to indicate that the process occurs at constant pressure
When heat is added to a system, this reaction is __________ and the value of q is __________. When heat is removed from a system, this reaction is __________ and the value of q is __________.
-endothermic -positive -exothermic -negative
When energy flows from the system to the surroundings, the reaction is __________. When the energy flows from the surroundings to the system, the reaction is __________.
-exothermic -endothermic
An endothermic reaction occurs when bonds __________ and energy is __________. An exothermic reaction occurs when bonds __________ and energy is __________.
-form -absorbed -break -released
q is called __________ and represents __________ directly because of a difference in temperature. If q is positive, the reaction is __________, and if q is negative, the reaction is __________.
-heat -energy transferred -endothermic -exothermic
Energy transfer in the form of heat always flows from the __________ object to the __________ object.
-hotter -colder
Gram for gram, __________ has many times the fuel value of __________.
-hydrogen -carbon
If a system is heated by its surroundings, then q is __________. When work is done by the system, w is __________ and the internal energy __________. If energy is transferred from the system into the surroundings due to a temperature difference, then q is _________ and the internal energy __________.
-positive -negative -decreases -negative -decreases
If electrostatic potential energy is positive, then the particles __________ each other. If it is negative, then the particles __________ each other. A lower electrostatic potential energy (aka a more negative value) has __________ stability, so particles that attract each other because of their charges form an arrangement with a(n) __________ electrostatic potential energy than particles that repel each other.
-repel -attract -greater -lower
The enthalpy change that takes place at constant pressure when 1 mole of a substance is formed from its constituent elements in their standard states is the __________. A reaction that fits this description is known as a(n) __________.
-standard enthalpy of formation -formation reaction
At the molecular level, __________ and __________ dominate the relation between kinetic and potential energies. Temperature governs __________ at this level. Chemical bonds and different electric charges cause __________ that give rise to the potential energy stored in the arrangements of the atoms, ions, and molecules in matter.
-temperature -charge -motion -interactions between particles
What is the standard enthalpy of formation for any element in its standard state?
0 kJ
2ClF + O2 --> Cl2 + F2O ΔH1 = 167.4 kJ 2ClF3 + 2O2 --> Cl2O + 3F2O ΔH2 = 341.1 kJ 2F2 + O2 --> 2F2O ΔH3 = -43.4 kJ Use the above data to calculate ΔH for the following reaction. ClF + F2 --> ClF3
1 - Multiply reaction 1 by 1/2 ClF + 1/2O2 --> 1/2Cl2 + 1/2F2O 1/2ΔH1 = 83.7 kJ 2 - Multiply reaction 3 by 1/2 F2 + 1/2O2 --> F2O 1/2ΔH3 = -21.7 kJ 3 - Multiply reaction 2 by 1/2 and flip (including changing the sign of ΔH 1/2Cl2O + 3/2F2O --> ClF3 + O2 1/2ΔH = -170.6 kJ 4 - Sum the reactions, cancelling out what cancels ANSWER: ClF + F2 --> ClF3 ΔH = 83.7kJ - 21.7 kJ - 170.6 kJ = ΔH = -108.6 kJ
Protons (H+) and nitrosonium ions (NO+) react with fluoride ions (F-) in the gas phase under laboratory conditions (constant temperature and pressure) to form HF and NOF, respectively. 1) At a given temperature, which ion has the greatest kinetic energy? 2) Which cation is moving at the higher average speed?
1) All of the ions have the same kinetic energy because the temperature is constant 2) The protons (H+) are moving at a higher speed because they have a much lower mass than NO+
Overall Heat Capacity 1) Define 2) Abbreviation 3) Label
1) Heat capacity per calorimeter 2) C 3) J / K
Specific Heat Capacity 1) Define 2) Abbreviation 3) Label 4) Specific Heat Capacity Equation
1) Heat capacity per gram 2) s 3) J / K⋅g 4) q = msΔT
Molar Heat Capacity 1) Define 2) Abbreviation 3) Label 4) Molar Heat Capacity Equation
1) Heat capacity per mole 2) c 3) J / K⋅mole 4) q = ncΔT
Joule 1) Define 2) Equivalency with calorie
1) The SI unity of energy 2) 4.184 J = 1 cal
The reaction below shows the formation of NO. This is a constant pressure process. N2(g) + O2(g) --> 2NO(g) ΔH = 180 kJ 1) What is the heat involved in this process? 2) Is this an exothermic or endothermic reaction? 3) Does energy flow into the system or out of the system?
1) ΔH = q (at constant pressure) = 180 kJ 2) Endothermic (because bonds are forming and q is positive 180 rather than negative 180) 3) Into (because bonds are forming and it is endothermic)
Between periods of a hockey game, an ice resurfacing machine spreads 855 L of water across the surface of a hokey rink. 1) If the system is the water, what is the signs of ΔH of the system as the water freezes? 2) To freeze this volume of water at 0°C, what is the value of ΔH of the system? The density of water is 1.00 g/mL, and ΔH of a solid = -6.01 kJ/mol.
1: -Negative (because it is an exothermic process because the water is freezing) 2: - 855 L ( 1000 mL / L ) ( 1.00 g / mL ) ( mol / 18.02 g H2O ) = 47447 mol H2O - 47447 mol H2O ( -6.01 kJ/mol) = -2.85 x 10^5 kJ
Alkanes with ___ or more carbon atoms can be branched-chain hydrocarbons
4
Bomb Calorimeter
A constant-volume device used to measure the energy released during a combustion reaction
Show how we could combine reactions A and B below to get reaction C. How is ΔHC related to the values of ΔHA and ΔHB? A: maltose + H2O --> 2glucose ΔHA B: 6CO2 + 6H2O --> glucose + 6O2 ΔHB C: maltose + 12O2 --> 12CO2 + 11H2O ΔHC
A: maltose + H2O --> 2glucose ΔHA B: 2glucose + 12O2 --> 12CO2 + 12H2O -2ΔHB ----------------------------------------------------- C: maltose + 12O2 --> 12CO2 + 11H2O ΔHC ΔHC = ΔHA - 2ΔHB
Use reactions B and C to calculate the ΔH for reaction A. A: 2CH4 + 3O2 --> 2CO + 4H2O ΔHA = ? B: CH4 + 2O2 --> CO2 + 2H2O ΔHB = -802 kJ C: 2CO + O2 --> 2CO2 ΔHC = -566 kJ
B: 2CH4 + 4O2 --> 2CO2 + 4H2O ΔHB = -1604 kJ C: 2CO2 --> 2CO + O2 ΔHC = 566 kJ ------------------------------------------------------------ A: 2CH4 + 3O2 --> 2CO + 4H2O ΔHA = -1038 kJ
Determine the unknown ΔH given the following reactions. A: C + O2 --> CO2 ΔH = -393.5 kJ B: C + 1/2O2 --> CO ΔH = ? C: CO + 1/2O2 --> CO2 ΔH = -283.0 kJ
B: C + 1/2O2 --> CO ΔH = ? C: CO + 1/2O2 --> CO2 ΔH = -283.0 kJ ----------------------------------------------- A: C + O2 --> CO2 ΔH = -393.5 kJ ΔH? = -393.5 kJ - -283.0 kJ = ΔH? = -110.5 kJ
Give an example of an experiment carried out at a constant volume.
Bomb Calorimetry
What is the equation for the energy (as heat) released by a reaction?
E = msΔT E = energy (as heat) released by a reaction s = specific heat capacity of the solution m = mass of the solution ΔT = change in temperature of the solution
What is defined as the capacity to do work or produce heat?
Energy
Endothermic
Energy / heat is absorbed into the system from the surroundings
Exothermic
Energy / heat is released from a system
Law of Conservation of Energy
Energy can be converted from one form to another but cannot be created or destroyed
Molar Enthalpy of Vaporization (define & equation)
Energy change going from a liquid to a gas q = nΔHvap
Molar Enthalpy of Fusion (define & equation)
Energy change going from a solid to liquid q = nΔHfus
Surroundings
Everything that is not part of the system
When water freezes, is it an exothermic or endothermic reaction?
Exothermic
Many automobiles run on either gasoline or diesel fuel. Both fuels are mixtures, but the energy content in gasoline can be approximated by a hydrocarbon with the formula C9H20 (d = 0.718 g/mL). Diesel fuel may be considered to be C14H30 (d = 0.763 g/mL). Using these 2 formulas, calculate the fuel value per gram of each fuel and the fuel density per liter of each fuel. ΔH°comb C9H20 = 6160 kJ/mol ΔH°comb C14H30 = 7940 kJ/mol
FUEL VALUES: C9H20: (6160 kJ/mol) (mol / 28.25 g) = 48.0 kJ/g C9H20 C14H30: (7940 kJ/mol) (mol / 198.238 g) = 40.1 kJ/g C14H30 FUEL DENSITIES: C9H20: (48.0 kJ/mol) (0.718 g / mL) (1000 mL / L ) = 34500 kJ/L C9H20 C14H30: (40.1 kJ / g) (0.763 g / mL) (1000 mL / L) = 30600 kJ/L C14H30
T or F The energy of the universe is increasing.
False
T or F The products of an endothermic reaction have less energy than the reactants.
False
T or F The more positive the enthalpy of formation (ΔH°f) of a substance, the more stable it is.
False - The more NEGATIVE, the more stable it is
T or F In calorimeters that allow the volume to change while the pressure remains constant, q calorimeter is different than the ΔHrxn.
False - q calorimeter is THE SAME AS ΔHrxn when the volume changes but pressure remains constant
Enthalpy Equation
H = E + PV
What is the name given to the constant which relates the amount of heat absorbed to the temperature change?
Heat Capacity
Calorimetry
Measuring heat based on observing temperature change
Use Hess's Law to find the ΔH in the overall reaction of: N2(g) + 2O2(g) --> 2NO2(g) ΔH1 = ? given the following information: N2(g) + O2(g) --> 2NO(g) ΔH2 = 180 kJ 2NO(g) + O2(g) --> 2NO2(g) ΔH3 = -112 kJ
N2(g) + O2(g) --> 2NO(g) ΔH2 = 180 kJ 2NO(g) + O2(g) --> 2NO2(g) ΔH3 = -112 kJ ----------------------------------------------- N2(g) + 2O2(g) --> 2NO2(g) ΔH1 = ΔH2 + ΔH3 = 68 kJ Both of the "2NO2's" are cancelled out of the first and second equations to get the final equation that we are looking for
When a system expands, is the sign of the work positive or negative?
Negative w = -PΔV
Fuel Value
Quantity of energy released during the complete combustion of 1 gram of a substance (just multiply the ΔH by their molar mass to get kJ/g)
