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Questions and Answers
What does the symbol '∆Hsolid' represent in the context of the provided text?
What does the symbol '∆Hsolid' represent in the context of the provided text?
- The heat capacity of water at its freezing point.
- The change in kinetic energy during a phase transition.
- The specific heat of water in the solid phase.
- The enthalpy of solidification of water. (correct)
Using the provided calculations, what is the total energy, in kilojoules, lost when 855 L of water freezes?
Using the provided calculations, what is the total energy, in kilojoules, lost when 855 L of water freezes?
- $-6.01 \times 10^4$ kJ
- $-2.85 \times 10^4$ kJ
- $-2.85 \times 10^5$ kJ (correct)
- $4.745 \times 10^4$ kJ
Which formula is used to calculate the heat required for a temperature change?
Which formula is used to calculate the heat required for a temperature change?
- $q = m c_s\Delta T$
- $q = n\Delta H_{vap}$
- $q = nC_P\Delta T$ (correct)
- $q = n\Delta H_{fus}$
What is the primary difference between molar heat capacity (cP) and specific heat capacity (cs)?
What is the primary difference between molar heat capacity (cP) and specific heat capacity (cs)?
According to the heating curve diagram, during a phase change, such as from a solid to a liquid, what happens to the temperature when heat is added?
According to the heating curve diagram, during a phase change, such as from a solid to a liquid, what happens to the temperature when heat is added?
Which of the following best describes potential energy?
Which of the following best describes potential energy?
According to the principles of energy, what is the primary difference between kinetic and potential energy?
According to the principles of energy, what is the primary difference between kinetic and potential energy?
The formula for kinetic energy is given by $KE = \frac{1}{2}mu^2$. What does 'u' represent in this equation?
The formula for kinetic energy is given by $KE = \frac{1}{2}mu^2$. What does 'u' represent in this equation?
The total energy of a system is the sum of what two types of energy?
The total energy of a system is the sum of what two types of energy?
What does the law of conservation of energy state?
What does the law of conservation of energy state?
Which factor primarily influences the kinetic energy of molecules at the molecular level?
Which factor primarily influences the kinetic energy of molecules at the molecular level?
In the context of systems and surroundings, which of the following describes a closed system?
In the context of systems and surroundings, which of the following describes a closed system?
What indicates an exothermic reaction regarding heat flow?
What indicates an exothermic reaction regarding heat flow?
What is the relationship between heat absorbed by a system and the kinetic energy of its molecules?
What is the relationship between heat absorbed by a system and the kinetic energy of its molecules?
Which of the following is a state function?
Which of the following is a state function?
Which of the following is NOT a type of molecular motion?
Which of the following is NOT a type of molecular motion?
A system performs work on its surroundings. Which of the following is true about the sign of work (w) in the equation $ΔE = q + w$?
A system performs work on its surroundings. Which of the following is true about the sign of work (w) in the equation $ΔE = q + w$?
Which of these statements about the first law of thermodynamics is correct?
Which of these statements about the first law of thermodynamics is correct?
If a gas expands against a constant external pressure, which statement is true regarding the change of volume $ΔV$ and the work done?
If a gas expands against a constant external pressure, which statement is true regarding the change of volume $ΔV$ and the work done?
A system has $ΔE = -100 J$ and $q = 50 J$. What is the work (w) done by or on the system, in joules?
A system has $ΔE = -100 J$ and $q = 50 J$. What is the work (w) done by or on the system, in joules?
A gas expands from 10 L to 20 L against a constant external pressure of 2 atm. What is the work done in Joules?
A gas expands from 10 L to 20 L against a constant external pressure of 2 atm. What is the work done in Joules?
When water freezes, is the change in enthalpy ($\Delta H_{sys}$) of the water positive or negative?
When water freezes, is the change in enthalpy ($\Delta H_{sys}$) of the water positive or negative?
If 855 L of water freezes, what is the approximate value of the change in enthalpy ($\Delta H_{sys}$)? (Density of water is 1.00 g/mL, $\Delta H_{solid}$ = -6.01 kJ/mol)
If 855 L of water freezes, what is the approximate value of the change in enthalpy ($\Delta H_{sys}$)? (Density of water is 1.00 g/mL, $\Delta H_{solid}$ = -6.01 kJ/mol)
In this scenario, what does $\Delta H_{sys}$ represent?
In this scenario, what does $\Delta H_{sys}$ represent?
If the process of freezing water is considered at a constant pressure, how does the change in enthalpy ($\Delta H_{sys}$) relate to the heat ($q_P$)?
If the process of freezing water is considered at a constant pressure, how does the change in enthalpy ($\Delta H_{sys}$) relate to the heat ($q_P$)?
What is the first step in calculating the change of enthalpy when freezing 855 L of water?
What is the first step in calculating the change of enthalpy when freezing 855 L of water?
Using the density of water at 1.00 g/mL, what is the mass of 855 L of water?
Using the density of water at 1.00 g/mL, what is the mass of 855 L of water?
What is the molar mass of water ($H_2O$) needed for the calculation?
What is the molar mass of water ($H_2O$) needed for the calculation?
If the enthalpy of solidification for water is -6.01 kJ/mol, what does the negative sign indicate?
If the enthalpy of solidification for water is -6.01 kJ/mol, what does the negative sign indicate?
Given the reaction $C_2H_4 + H_2 \rightarrow C_2H_6$, and using Hess's Law, what is the correct formula to calculate $ \Delta H_{rxn}$?
Given the reaction $C_2H_4 + H_2 \rightarrow C_2H_6$, and using Hess's Law, what is the correct formula to calculate $ \Delta H_{rxn}$?
What does the symbol $\Delta H_f^\circ$ represent?
What does the symbol $\Delta H_f^\circ$ represent?
What are the correct standard conditions for a standard enthalpy change?
What are the correct standard conditions for a standard enthalpy change?
Which of the following equations represents the standard enthalpy of formation $\Delta H_f^\circ$ for water?
Which of the following equations represents the standard enthalpy of formation $\Delta H_f^\circ$ for water?
How can the standard enthalpy of reaction be calculated using standard enthalpies of formation?
How can the standard enthalpy of reaction be calculated using standard enthalpies of formation?
What is the classification of hydrocarbons where each carbon atom is bonded to 4 other atoms?
What is the classification of hydrocarbons where each carbon atom is bonded to 4 other atoms?
Which of the following ways cannot be used to determine the standard enthalpy of reaction, $ \Delta H^\circ_{rxn}$?
Which of the following ways cannot be used to determine the standard enthalpy of reaction, $ \Delta H^\circ_{rxn}$?
In the calculation of $\Delta H_{rxn} = -285.8 \text{ kJ} + (-1441 \text{ kJ}) + 1560 \text{ kJ}$, what does the positive sign in +1560 kJ signify?
In the calculation of $\Delta H_{rxn} = -285.8 \text{ kJ} + (-1441 \text{ kJ}) + 1560 \text{ kJ}$, what does the positive sign in +1560 kJ signify?
Given the reaction $2NO(g) \rightarrow N_2(g) + O_2(g)$ with $\Delta H = -180 kJ$, what is the $\Delta H$ for the reaction $4NO(g) \rightarrow 2N_2(g) + 2O_2(g)$?
Given the reaction $2NO(g) \rightarrow N_2(g) + O_2(g)$ with $\Delta H = -180 kJ$, what is the $\Delta H$ for the reaction $4NO(g) \rightarrow 2N_2(g) + 2O_2(g)$?
According to Hess's Law, how should the enthalpy change ($\Delta H$) of a reaction be modified if the reaction is reversed?
According to Hess's Law, how should the enthalpy change ($\Delta H$) of a reaction be modified if the reaction is reversed?
If reaction $A \rightarrow B$ has $\Delta H = -100 kJ$ and $B \rightarrow C$ has $\Delta H = 50 kJ$, what is the $\Delta H$ of the overall reaction $A \rightarrow C$?
If reaction $A \rightarrow B$ has $\Delta H = -100 kJ$ and $B \rightarrow C$ has $\Delta H = 50 kJ$, what is the $\Delta H$ of the overall reaction $A \rightarrow C$?
Given the following reactions: 1) $H_2(g) + \frac{1}{2} O_2(g) \rightarrow H_2O(l)$ $\Delta H = -285.8 kJ$ and 2) $C_2H_4(g) + 3O_2(g) \rightarrow 2H_2O(l) + 2CO_2(g) $ $\Delta H=-1411 kJ$. What is the correct way to manipulate them to find the $\Delta H$ of $C_2H_4(g) + H_2(g) \rightarrow C_2H_6(g)$?
Given the following reactions: 1) $H_2(g) + \frac{1}{2} O_2(g) \rightarrow H_2O(l)$ $\Delta H = -285.8 kJ$ and 2) $C_2H_4(g) + 3O_2(g) \rightarrow 2H_2O(l) + 2CO_2(g) $ $\Delta H=-1411 kJ$. What is the correct way to manipulate them to find the $\Delta H$ of $C_2H_4(g) + H_2(g) \rightarrow C_2H_6(g)$?
Consider the reaction $C_2H_6(g) + \frac{7}{2} O_2(g) \rightarrow 3 H_2O(l) + 2 CO_2(g)$ with $\Delta H =-1560 kJ$. What is the $\Delta H$ for the reaction $3H_2O(l) + 2CO_2(g) \rightarrow C_2H_6(g) + \frac{7}{2} O_2(g)$?
Consider the reaction $C_2H_6(g) + \frac{7}{2} O_2(g) \rightarrow 3 H_2O(l) + 2 CO_2(g)$ with $\Delta H =-1560 kJ$. What is the $\Delta H$ for the reaction $3H_2O(l) + 2CO_2(g) \rightarrow C_2H_6(g) + \frac{7}{2} O_2(g)$?
Given the reactions: 1) $H_2(g) + \frac{1}{2} O_2(g) \rightarrow H_2O(l)$ $\Delta H_1 = -285.8 kJ$ , 2) $C_2H_4(g) + 3 O_2(g) \rightarrow 2 H_2O(l) + 2 CO_2(g)$ $\Delta H_2 = -1411 kJ$ and 3) $C_2H_6(g) + \frac{7}{2} O_2(g) \rightarrow 3 H_2O(l) + 2 CO_2(g)$ $\Delta H_3 = -1560 kJ$, what is the correct set up to calculate $\Delta H$ for $C_2H_4(g) + H_2(g) \rightarrow C_2H_6(g)$?
Given the reactions: 1) $H_2(g) + \frac{1}{2} O_2(g) \rightarrow H_2O(l)$ $\Delta H_1 = -285.8 kJ$ , 2) $C_2H_4(g) + 3 O_2(g) \rightarrow 2 H_2O(l) + 2 CO_2(g)$ $\Delta H_2 = -1411 kJ$ and 3) $C_2H_6(g) + \frac{7}{2} O_2(g) \rightarrow 3 H_2O(l) + 2 CO_2(g)$ $\Delta H_3 = -1560 kJ$, what is the correct set up to calculate $\Delta H$ for $C_2H_4(g) + H_2(g) \rightarrow C_2H_6(g)$?
Using the given reactions: 1) $H_2(g) + \frac{1}{2} O_2(g) \rightarrow H_2O(l)$, $\Delta H_1 = -285.8 kJ$, 2) $C_2H_4(g) + 3O_2(g) \rightarrow 2H_2O(l) + 2CO_2(g)$, $\Delta H_2 = -1411 kJ$, and 3) $C_2H_6(g) + \frac{7}{2} O_2(g) \rightarrow 3H_2O(l) + 2CO_2(g)$, $\Delta H_3 = -1560 kJ$, what is the enthalpy change for the reaction $C_2H_4(g) + H_2(g) \rightarrow C_2H_6(g)$?
Using the given reactions: 1) $H_2(g) + \frac{1}{2} O_2(g) \rightarrow H_2O(l)$, $\Delta H_1 = -285.8 kJ$, 2) $C_2H_4(g) + 3O_2(g) \rightarrow 2H_2O(l) + 2CO_2(g)$, $\Delta H_2 = -1411 kJ$, and 3) $C_2H_6(g) + \frac{7}{2} O_2(g) \rightarrow 3H_2O(l) + 2CO_2(g)$, $\Delta H_3 = -1560 kJ$, what is the enthalpy change for the reaction $C_2H_4(g) + H_2(g) \rightarrow C_2H_6(g)$?
Which of the following statements best describes Hess's Law?
Which of the following statements best describes Hess's Law?
Flashcards
Molar heat of fusion (∆Hfus)
Molar heat of fusion (∆Hfus)
The amount of energy required to convert 1 mole of a solid at its melting point into the liquid state.
Molar heat of vaporization (∆Hvap)
Molar heat of vaporization (∆Hvap)
The amount of energy required to convert 1 mole of a liquid at its boiling point to the vapor state.
Molar heat capacity (cP)
Molar heat capacity (cP)
The quantity of energy required to raise the temperature of 1 mole of a substance by 1℃.
Specific heat (cs)
Specific heat (cs)
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Heat capacity (CP)
Heat capacity (CP)
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Internal Energy (E)
Internal Energy (E)
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State Function
State Function
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Change in Internal Energy (ΔE)
Change in Internal Energy (ΔE)
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Calorie (cal)
Calorie (cal)
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Joule (J)
Joule (J)
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First Law of Thermodynamics
First Law of Thermodynamics
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Work (w)
Work (w)
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Law of Conservation of Energy
Law of Conservation of Energy
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Potential Energy (PE)
Potential Energy (PE)
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Kinetic Energy (KE)
Kinetic Energy (KE)
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Total Energy
Total Energy
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Thermal Energy
Thermal Energy
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System
System
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Exothermic Process
Exothermic Process
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Endothermic Process
Endothermic Process
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Enthalpy change at constant pressure (∆Hsys)
Enthalpy change at constant pressure (∆Hsys)
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What does the sign of ∆Hsys tell us?
What does the sign of ∆Hsys tell us?
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Freezing
Freezing
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Enthalpy of solidification (∆Hsolid)
Enthalpy of solidification (∆Hsolid)
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Why is ∆Hsys negative for freezing?
Why is ∆Hsys negative for freezing?
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Volume to mass conversion
Volume to mass conversion
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Mass to mole conversion
Mass to mole conversion
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Calculating ∆Hsys for freezing water
Calculating ∆Hsys for freezing water
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Hess's Law of Constant Heat Summation
Hess's Law of Constant Heat Summation
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Hess's Law
Hess's Law
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Enthalpy Change for the Reverse Reaction
Enthalpy Change for the Reverse Reaction
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Hess's Law: Enthalpy is a State Function
Hess's Law: Enthalpy is a State Function
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Exothermic reaction
Exothermic reaction
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Endothermic reaction
Endothermic reaction
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Enthalpy change (H)
Enthalpy change (H)
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Standard Enthalpy of Formation (ΔHf°)
Standard Enthalpy of Formation (ΔHf°)
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Standard Enthalpy of Reaction (ΔH°rxn)
Standard Enthalpy of Reaction (ΔH°rxn)
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Standard State of a Substance
Standard State of a Substance
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Alkanes
Alkanes
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Relationship between Enthaply of formation and enthaply of reaction
Relationship between Enthaply of formation and enthaply of reaction
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Calorimetry
Calorimetry
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Study Notes
Chapter 6: Thermochemistry: Energy Changes in Reactions
- Thermochemistry is the study of the relationship between chemical reactions and changes in energy.
- Thermodynamics is the study of energy and its transformations.
- Thermal equilibrium is a state where temperature is uniform throughout a material, and no energy flows between points.
- Heat is energy transferred between objects due to a temperature difference.
- Work is a form of energy required to move an object through a distance; calculated as work (w) = force (F) x distance (d).
- Potential energy (PE) is energy stored due to position; PE = m x g x h, where m = mass, g = acceleration due to gravity, and h = vertical distance.
- Kinetic energy (KE) is energy due to motion; KE = 1/2mu², where m = mass and u = velocity.
- Total energy is the sum of potential and kinetic energy: Total energy = PE + KE = mgh + ½mu².
- Law of conservation of energy: Energy cannot be created or destroyed but can be converted from one form to another.
- Chemical energy is a form of potential energy that can be converted to heat.
- Thermal energy is the kinetic energy of atoms, ions, and molecules.
- Energy at the molecular level: Kinetic energy is related to mass, velocity, and temperature, while potential energy is related to electrostatic interactions (Q1 x Q2) /d, where Q = charge and d = distance).
- Electrostatic potential energy (Eel) is the energy stored between interacting charges; Eel ∝(Q1 x Q2) /d .
- Energy of Chemical Reactions: Energy is released or absorbed during reaction; the reactions are represented by chemical equations to show energy transfers.
- Terminology of Energy Transfer:
- System is the focus of the study, and a system.
- Isolated: No energy or matter exchanged with surroundings.
- Closed: Energy exchanged, but not matter. - Open: Both energy and matter exchanged.
- Surroundings: Everything outside the system.
- Universe is the system + surroundings.
- Examples of Systems:
- Isolated: Thermos bottle with tightly closed lid.
- Closed: Coffee cup with a lid.
- Open: Open cup of hot soup.
- Heat Flow:
- Exothermic: Energy flows out of the system to the surroundings (q < 0).
- Endothermic: Energy flows into the system from the surroundings (q > 0).
- Phase Changes and Heat Flow: The diagram shows different energy transfers between states (Solid, Liquid, Vapor). Specific changes (fusion, vaporization, solidification, condensation, sublimation, deposition) are also included in the diagram
- Energy and Phase Changes: The absorbed heat increases the kinetic energy of molecules. Loss of kinetic energy is caused by release of heat by molecules.
Change in Internal Energy
- ΔE = change in system's internal energy
- ΔE = q + w (q = heat, w = work)
- Work (w) = -PΔV (P = pressure, ΔV = change in volume)
- Work done by the system is considered negative.
Units of Energy
- Calorie (cal): Amount of heat required to raise the temperature of 1 gram of water by 1°C.
- Joule (J): SI unit of energy; 4.184 J = 1 cal
- Energy is heat and/or work.
First Law of Thermodynamics
- Energy of the universe is constant.
- Energy gained or lost by a system must equal the energy lost or gained by the surroundings; ΔEsystem= -ΔEsurroundings
Energy Flow Diagram
- Heat in (q > 0) flows to the system.
- Heat out (q < 0) flows from the system.
- Work done on the system (w > 0).
- Work done by the system (w < 0).
- ΔE = q + w
Enthalpy, Change in Enthalpy
- Enthalpy (H): Enthalpy is a state function. H = E + PV
- ΔH = ΔE + PΔV
- ΔH = qp (qp equals heat at constant pressure)
- ΔH > 0: Endothermic; ΔH < 0: Exothermic
- Subscripts are used to specify the process.
Calorimetry
- Calorimetry measures the transfer of heat.
- A calorimeter is a device to measure heat transfer in physical or chemical processes. In a closed system: -qsystem = qcalorimeter.
- Bomb calorimeter: Used to measure energy released during combustion reactions.
- The heat produced by a reaction is equal to the heat gained by the calorimeter, qrxn = qcal = Ccal ΔT, where Ccal is the heat capacity of the calorimeter and ΔT is the change in temperature.
Enthalpy in Change of State
- Molar heat of fusion ΔHfus: Energy to convert 1 mole of solid to liquid at its melting point; q = nΔHfus
- Molar heat of vaporization ΔHvap: Energy to convert 1 mole of liquid to vapor at its boiling point; q = nΔHvap
Heats of Reaction
- The heat involved in a reaction depends on the specific reaction involved (the reagents and products).
Hess's Law
- ΔHrxn for a sum of reactions equal to the sum of the ΔH values for the individual reactions.
- If a reaction is reversed the sign of ΔH changes
- If coefficients of a reaction are multiplied the value of ΔH is also multiplied.
Enthalpy of Formation, ΔH°f
- Standard enthalpy of formation, ∆H°f: enthalpy change when 1 mole of substance is formed from its elements in their standard states.
- Formation reaction for water: H2(g) + ½O2(g) → H₂O(l)
- Standard state: The most stable form of a substance under standard conditions. Standard conditions are 1 bar pressure and a given temperature, usually 25°C.
Standard Enthalpy of Reaction, ΔHrxn°
- Calculated from ΔH°f
- ΔH°rxn = ΣnproductsΔH°f - ΣnreactantsΔH°f, n = number of moles. - Tables listing the standard enthalpies of formation for many substances are commonly used to make calculations.
Alkanes
- Alkanes are hydrocarbons where each carbon atom is bonded to four other atoms.
- Alkane names are derived from prefixes based on the number of carbons in the molecule.
- Chemical formulas for alkanes: CnH2n+2
Fuel Values
- Fuel value: The energy released during complete combustion of 1 g of a substance.
- Fuel density: The energy released during complete combustion of 1 L of a liquid fuel.
- Tables listing fuel values (kJ/g) are available.
Food Values
- Food value: The energy produced when a material is completely consumed by an organism for sustenance.
- Determined by bomb calorimetry.
- Nutritional calorie = 1 kcal = 4.184 kJ
Other Topics:
- Heating curves graphs the temperature change over time of a material as heat is added.
- Cooling curves show temperature decrease over time with heat transfer.
- Specific heat and Molar heat capacities: describe the energy required to change the temperature of a substance per gram/mole.
- Models of different types of molecules are presented.
- Tables show values for different materials.
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