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Questions and Answers

What does the subscript 'p' indicate in the molar heat capacity formula, Cp?

  • Constant pressure (correct)
  • Constant volume
  • Constant mass
  • Constant temperature

    • Molar heat capacity is only dependent on the temperature of the substance.

    False

    What is the formula to calculate the amount of heat absorbed by a substance?

    q = mcΔT

    In calorimetry, the equation qsystem = - qsurroundings is used to represent the _____ of heat.

    <p>transfer</p> Signup and view all the answers

    Match the following quantities with their respective descriptions:

    <p>Cp = Molar heat capacity at constant pressure q = Amount of heat energy ΔT = Change in temperature Ccalorimeter = Calorimeter constant</p> Signup and view all the answers

    What happens to the temperature of a calorimeter during a reaction?

    <p>It increases</p> Signup and view all the answers

    Calculate q for a 24.0 g aluminum can heated by 15.0°C if its specific heat is 0.897 J g-1 °C-1.

    <p>q = 24.0 g * 0.897 J g-1 °C-1 * 15.0°C = 323.88 J</p> Signup and view all the answers

    In an ideal calorimetry measurement, the heat lost by a system is equal to the heat gained by the surroundings.

    <p>True</p> Signup and view all the answers

    What is the specific heat capacity represented by?

    <p>c</p> Signup and view all the answers

    Energy can be created from one form to another according to the first law of thermodynamics.

    <p>False</p> Signup and view all the answers

    What does DE represent in the context of energy flow?

    <p>Change in energy of the system</p> Signup and view all the answers

    Calorimetry measures the flow of heat into and out of a _______.

    <p>system</p> Signup and view all the answers

    Match the types of heat capacities with their definitions:

    <p>c = Specific heat capacity Cp = Molar heat capacity ΔT = Temperature change m = Mass of the substance</p> Signup and view all the answers

    If 515 J of heat is added to a gas and it does 218 J of work, what is the change in energy of the system?

    <p>297 J</p> Signup and view all the answers

    Negative values for energy change indicate that energy is absorbed by the system.

    <p>False</p> Signup and view all the answers

    What is thermal pollution?

    <p>Temperature change in a body of water from waste streams.</p> Signup and view all the answers

    What is the energy density of the fuel if 0.245 g of it produces a temperature increase of 5.23°C in a calorimeter, given that the heater supplies 100.0 J of heat for a temperature increase of 0.850°C?

    <p>4000 J/g</p> Signup and view all the answers

    The heat flow during a phase change occurs with a change in temperature.

    <p>False</p> Signup and view all the answers

    What is the formula for energy change (ΔE) in terms of heat flow (q) and work (w)?

    <p>ΔE = q + w</p> Signup and view all the answers

    The combustion of octane under constant volume conditions releases _____ kJ.

    <p>5.45 x 10^3</p> Signup and view all the answers

    Match the type of process with its corresponding ΔH sign:

    <p>Exothermic = Negative Endothermic = Positive Heat of Vaporization = Positive Heat of Condensation = Negative</p> Signup and view all the answers

    What term describes the heat required to convert liquid to gas?

    <p>Heat of Vaporization</p> Signup and view all the answers

    Enthalpy change (ΔH) is positive for exothermic processes.

    <p>False</p> Signup and view all the answers

    What does ΔH represent in thermodynamics?

    <p>Enthalpy change</p> Signup and view all the answers

    What is the primary relationship between a nation's energy consumption and its economic growth?

    <p>Directly proportional</p> Signup and view all the answers

    Nearly half of all domestic energy use in the United States is dedicated to producing electricity.

    <p>True</p> Signup and view all the answers

    What is the first law of thermodynamics?

    <p>Energy cannot be created or destroyed, only transformed from one form to another.</p> Signup and view all the answers

    In 2011, the total energy supply for the United States was ______ quadrillion Btu.

    <p>107.66</p> Signup and view all the answers

    Match each category of energy consumption with its percentage in the United States in 2011:

    <p>Residential = 22% Commercial = 19% Industrial = 31% Transportation = 28%</p> Signup and view all the answers

    What type of energy is characterized by the position of an object?

    <p>Potential energy</p> Signup and view all the answers

    What is meant by 'conversion losses' in energy generation?

    <p>Conversion losses refer to the energy that is lost when energy is transformed from one form to another during generation.</p> Signup and view all the answers

    The energy supply in the U.S. is completely derived from domestic production.

    <p>False</p> Signup and view all the answers

    What does a negative change in energy (DE) indicate?

    <p>Energy is being released by the system</p> Signup and view all the answers

    Heat can be completely converted to work without any loss of energy.

    <p>False</p> Signup and view all the answers

    What is the first law of thermodynamics?

    <p>Energy can be transformed from one form to another but cannot be created or destroyed.</p> Signup and view all the answers

    Calorimetry is primarily used to measure the flow of heat into and out of a _______.

    <p>system</p> Signup and view all the answers

    Match the type of heat capacity with its description:

    <p>Specific heat capacity = Heat required to raise 1 gram of a substance by 1ºC Molar heat capacity = Heat required to raise 1 mole of a substance by 1ºC Heat capacity = Total heat required to raise the temperature of an entire sample Calorimeter = Device for measuring heat flow</p> Signup and view all the answers

    If 515 J of heat is added to a gas that does 218 J of work, what is the change in energy of the system?

    <p>297 J</p> Signup and view all the answers

    Thermal pollution is caused by the discharge of waste energy into bodies of water.

    <p>True</p> Signup and view all the answers

    What is waste energy?

    <p>Energy that is not converted to useful work and may contribute to thermal pollution.</p> Signup and view all the answers

    What is the primary difference between the heat of vaporization and the heat of condensation?

    <p>Heat of vaporization is endothermic, while heat of condensation is exothermic.</p> Signup and view all the answers

    The change in enthalpy (ΔH) is positive when a system releases heat.

    <p>False</p> Signup and view all the answers

    What is the relationship between internal energy change (DE), heat flow (q), and work (w)?

    <p>DE = q + w</p> Signup and view all the answers

    The energy density of a fuel is calculated as the amount of energy liberated per _____ of fuel burned.

    <p>gram</p> Signup and view all the answers

    Match the following process with their corresponding ΔH sign:

    <p>Exothermic = ΔH &lt; 0 Endothermic = ΔH &gt; 0</p> Signup and view all the answers

    Under what conditions does the heat flow during a phase change occur?

    <p>Constant pressure</p> Signup and view all the answers

    What is the enthalpy change (ΔH) for the combustion of 1 mole of methane?

    <p>-890.4 kJ</p> Signup and view all the answers

    The heat of formation for elements in their standard state is always greater than zero.

    <p>False</p> Signup and view all the answers

    The internal energy change for a reaction can be defined as the heat flow at constant pressure.

    <p>False</p> Signup and view all the answers

    What does ΔH represent in thermodynamics?

    <p>Enthalpy change</p> Signup and view all the answers

    What is the reaction type for CH4 + 2O2 -> CO2 + 2H2O?

    <p>exothermic</p> Signup and view all the answers

    The thermochemical equation indicates that if stoichiometric coefficients are multiplied by a factor, the heat of reaction must also be multiplied by that ______.

    <p>factor</p> Signup and view all the answers

    Match the types of heat of reaction with their descriptions:

    <p>ΔHcomb = Heat of combustion ΔHneut = Heat of neutralization ΔHf = Heat of formation ΔHrxn = General heat of reaction</p> Signup and view all the answers

    Which bonds are broken during the combustion of methane?

    <p>4 C-H bonds and 2 O=O bonds</p> Signup and view all the answers

    Hess's Law states that the total enthalpy change for a reaction is the same, regardless of the number of steps taken.

    <p>True</p> Signup and view all the answers

    What is the standard unit of ΔH for a phase change?

    <p>kJ/mol</p> Signup and view all the answers

    What is the standard state for an element?

    <p>The most stable form of an element at room temperature and pressure.</p> Signup and view all the answers

    The heat of vaporization for water is low and does not play a role in electricity production.

    <p>False</p> Signup and view all the answers

    What is the term for the enthalpy change that occurs during a chemical reaction?

    <p>heat of reaction</p> Signup and view all the answers

    Breaking bonds requires _____, while forming bonds releases _____ energy.

    <p>energy; energy</p> Signup and view all the answers

    Match the phase change with its corresponding enthalpy change:

    <p>Melting = ΔHfus Freezing = ΔHfus Vaporization = ΔHvap Condensation = ΔHvap</p> Signup and view all the answers

    How can the heat flow during phase changes be calculated?

    <p>Using the number of moles and enthalpy change</p> Signup and view all the answers

    Endothermic reactions release more energy than is required to break reactant bonds.

    <p>False</p> Signup and view all the answers

    What happens to the temperature during a phase change?

    <p>Remains constant</p> Signup and view all the answers

    What does a positive value of change in energy (DE) indicate?

    <p>Energy is being absorbed</p> Signup and view all the answers

    It is impossible to completely convert all heat to work.

    <p>True</p> Signup and view all the answers

    What is the main principle of the first law of thermodynamics?

    <p>Energy can be transformed, but not created or destroyed.</p> Signup and view all the answers

    Calorimetry measures the flow of heat into and out of a _______.

    <p>system</p> Signup and view all the answers

    Match the following factors to their descriptions concerning heat capacity:

    <p>m = Mass of the substance c = Specific heat capacity ΔT = Temperature change n = Number of moles</p> Signup and view all the answers

    Which of the following statements about waste energy is true?

    <p>Waste energy may lead to thermal pollution.</p> Signup and view all the answers

    Specific heat is the same for all substances regardless of their phase.

    <p>False</p> Signup and view all the answers

    What does the efficiency of conversion from heat to work represent?

    <p>The percentage of heat that is converted into useful work.</p> Signup and view all the answers

    What type of energy is associated with the position of an object?

    <p>Potential energy</p> Signup and view all the answers

    The Joule is the SI unit of energy.

    <p>True</p> Signup and view all the answers

    What is the flow of energy between two objects due to a temperature difference called?

    <p>Heat</p> Signup and view all the answers

    During energy transformation, the total energy must be _____

    <p>conserved</p> Signup and view all the answers

    Which of the following is a unit of energy besides Joules?

    <p>Calorie</p> Signup and view all the answers

    Match the following forms of energy with their descriptions:

    <p>Kinetic energy = Energy associated with motion Chemical energy = Energy released or absorbed in chemical reactions Thermal energy = Energy due to temperature differences Nuclear energy = Energy released during nuclear reactions</p> Signup and view all the answers

    Work in a chemical context is defined as the transfer of energy through a force moving a mass some distance.

    <p>True</p> Signup and view all the answers

    What must be specified to account for energy transformations and conversions?

    <p>System and surroundings</p> Signup and view all the answers

    What is the enthalpy change for an exothermic process?

    <p>ΔH &lt; 0</p> Signup and view all the answers

    The heat of condensation is always an endothermic process.

    <p>False</p> Signup and view all the answers

    What is the relationship between q, w, and ΔE?

    <p>ΔE = q + w</p> Signup and view all the answers

    The change in enthalpy (ΔH) during a phase change occurs with no change in __________.

    <p>temperature</p> Signup and view all the answers

    What is the heat of vaporization (ΔHvap)?

    <p>Heat ABSORBED to convert liquid to gas</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>q = Heat flow during a process ΔH = Change in enthalpy exothermic = Process that releases heat endothermic = Process that absorbs heat</p> Signup and view all the answers

    Combustion of octane under constant pressure conditions releases more energy than under constant volume conditions.

    <p>True</p> Signup and view all the answers

    What is the unit for enthalpy change (ΔH) during a phase change?

    <p>kJ/mol</p> Signup and view all the answers

    What happens to ΔH when a system absorbs heat?

    <p>ΔH &gt; 0</p> Signup and view all the answers

    The heat of vaporization for water is greater than the heat of fusion for ice.

    <p>True</p> Signup and view all the answers

    What type of reaction is it if the energy released from product bonds is greater than the energy required to break reactant bonds?

    <p>exothermic</p> Signup and view all the answers

    To calculate the heat flow during a phase change, the formula is ΔH = n × ΔH phase change, where n is the number of _____ of the substance.

    <p>moles</p> Signup and view all the answers

    Match the phase change with its corresponding ΔH sign:

    <p>Melting = Positive ΔH Freezing = Negative ΔH Vaporization = Positive ΔH Condensation = Negative ΔH</p> Signup and view all the answers

    What happens to the temperature during a phase change?

    <p>It remains constant</p> Signup and view all the answers

    What is the primary purpose of using the large heat of vaporization of water in power plants?

    <p>To convert chemical energy into electricity</p> Signup and view all the answers

    The enthalpy change for melting ice is negative.

    <p>False</p> Signup and view all the answers

    What type of reaction is the combustion of methane?

    <p>Exothermic reaction</p> Signup and view all the answers

    The ΔH value for the combustion of 1 mole of methane is -890.4 kJ.

    <p>True</p> Signup and view all the answers

    What is the heat of formation (ΔHf) for elements in their standard state?

    <p>0</p> Signup and view all the answers

    In a combustion reaction, carbon and hydrogen bonds are _____ while carbon dioxide and water are _____ during the process.

    <p>broken; formed</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>ΔHcomb = Heat of combustion ΔHneut = Heat of neutralization ΔHf = Heat of formation ΔHfus = Heat of fusion</p> Signup and view all the answers

    What must be done to the ΔH value if the stoichiometric coefficients in a reaction are multiplied by 2?

    <p>It is multiplied by 2</p> Signup and view all the answers

    What is Hess's Law used for?

    <p>To obtain heats of reaction indirectly.</p> Signup and view all the answers

    The bond energies used to calculate enthalpy changes are exact values.

    <p>False</p> Signup and view all the answers

    Study Notes

    Molar Heat Capacity

    • Defined as the heat needed to raise the temperature of one mole of a substance by 1ºC.
    • Represented by ( C_p ) (subscript "p" indicates constant pressure).
    • Specific to each compound and phase.

    Heat Capacity and Specific Heat

    • Heat absorbed can be calculated using the formula: ( q = mc\Delta T ) or ( q = nC_p\Delta T ).
    • Specific heat capacity (( c )) measures the heat required to raise the temperature of one gram of a substance by 1ºC.
    • Both specific heat and molar heat capacities vary by substance.

    Calorimetry

    • Heat flow measurement utilizes a calorimeter, which gauges heat absorbed or released by monitoring the surrounding temperature change.
    • Fundamental relationship: ( q_{\text{system}} = - q_{\text{surroundings}} ).
    • In calorimetric measurements, two main steps are performed: Calibration and Actual Measurement.

    Example Problems in Calorimetry

    • For a 24.0 g aluminum can heated by 15.0°C, calculate ( q ).
    • Molar heat capacity of liquid water is 75.3 J/(mol·K). For 37.5 g of water cooled from 42.0 to 7.0°C, determine ( q ).

    Energy Transformation and Conservation of Energy

    • Energy can change forms but not created or destroyed, expressed as ( \Delta E_{\text{universe}} = \Delta E_{\text{surroundings}} + \Delta E_{\text{system}} = 0 ).
    • Signs of energy change indicate flow direction: negative for release, positive for absorption.

    Waste Energy

    • Heat can be harnessed for work; however, complete conversion to work is unattainable. Residual heat is waste energy, contributing to thermal pollution.
    • Energy consumption efficiency can improve through enhanced energy efficiencies, affecting thermal pollution levels.

    Heat Capacity Factors

    • The amount of heat absorbed depends on:
      • Mass (( m )) or number of moles (( n )).
      • Type of material determined by specific heat (( c )) or molar heat capacity (( C_p )).
      • Temperature change (( \Delta T )).

    Enthalpy

    • Defined as heat flow under constant pressure conditions.
    • The equation for enthalpy change includes ( H = E + PV ) and ( \Delta H = q_p ).
    • Exothermic processes release heat, resulting in negative ( \Delta H ); endothermic processes absorb heat, yielding positive ( \Delta H ).

    ΔH of Phase Changes

    • Phase changes occur at constant pressure with no temperature change despite heat flow due to bond formation or breaking.
    • Heat of vaporization (( \Delta H_{\text{vap}} )) is endothermic; heat of condensation (( \Delta H_{\text{cond}} )) is exothermic.
    • The values of these enthalpy changes are equal in magnitude but opposite in sign: ( \Delta H_{\text{cond}} = -\Delta H_{\text{vap}} ).

    Chapter Objectives

    • Understanding energy conversions is crucial for economic growth; losses are inevitable in these processes.
    • Work and heat are defined using standard sign conventions; state functions play a significant role in thermodynamics.
    • The first law of thermodynamics can be expressed as ΔE_universe = ΔE_surroundings + ΔE_system = 0.
    • Calorimetric data can be utilized to determine energy (E) and enthalpy (H) values for chemical reactions.

    Energy Use and the World Economy

    • Energy consumption serves as an indicator of a nation's economic growth, directly linked to Gross Domestic Product (GDP).
    • In 2011, U.S. energy supply totaled 107.66 quadrillion Btu (British thermal units); 1 Btu = 1,054.35 J.
    • The energy supply breakdown includes coal, natural gas, crude oil, natural gas liquids (NGPL), nuclear, and renewable energy sources.
    • Domestic energy production was 70.47 quadrillion Btu, with imports making up 31.02 quadrillion Btu.
    • Energy consumption components in the U.S.: Residential (22%), Commercial (19%), Industrial (31%), and Transportation (28%).
    • Approximately half of domestic energy use is for electricity production; conversion losses account for nearly two-thirds of energy consumption in this process.

    Forms of Energy

    • Energy is categorized into potential energy and kinetic energy.
    • The relationship in energy change is given by the equation ΔE = q + w, where q is heat and w is work.

    Energy Transformation and Conservation

    • Energy flow direction is indicated by the sign of the energy change; negative values signify energy release, while positive values indicate energy absorption.
    • The first law of thermodynamics asserts that energy can change form but cannot be created or destroyed.

    Waste Energy

    • Waste energy is the leftover heat not converted into work, contributing to thermal pollution.
    • Conversion efficiency can be improved, balancing increased energy consumption.

    Heat Capacity and Calorimetry

    • Calorimetry measures heat transfer into and out of a system, influenced by mass (m), specific heat capacity (c), and temperature change (ΔT).
    • Specific heat capacity is the heat required to raise 1 gram of a substance by 1ºC; it is substance-specific.

    Enthalpy

    • Enthalpy change (ΔH) reflects heat flow under constant pressure; defined as H = E + PV.
    • Exothermic processes release heat (ΔH < 0), while endothermic processes absorb heat (ΔH > 0).

    ΔH of Phase Changes

    • Phase changes occur at constant pressure and are characterized by specific enthalpy values.
    • Heat of vaporization (ΔHvap) is endothermic; heat of condensation (ΔHcond) is exothermic, and ΔHcond = -ΔHvap.

    Bonds and Energy

    • Reactions involve breaking and forming bonds; bond breaking requires energy while bond formation releases energy.
    • The sign of ΔH indicates whether a reaction is exothermic or endothermic; for example, the combustion of methane releases 890.4 kJ.

    Heats of Reaction for Specific Reactions

    • Heats of reactions are labeled for different reactions, such as heat of combustion (ΔH_comb) and heat of neutralization (ΔH_neut).
    • ΔHf° is defined for the formation of one mole of a compound from elements in their standard state, where ΔHf° = 0 for elements in their most stable form.

    Hess’s Law and Heats of Reaction

    • Hess's law allows for determining heats of reaction indirectly when direct measurement is challenging or hazardous.

    Energy Definitions and Forms

    • Potential energy is related to an object's relative position, while kinetic energy is associated with an object's motion.
    • Kinetic energy formula: ( KE = \frac{1}{2} mv^2 ), where ( m ) is mass and ( v ) is velocity.
    • Internal energy consists of combined kinetic and potential energies of atoms and molecules.
    • Chemical energy is released or absorbed during chemical reactions.
    • Other energy forms include radiant, mechanical, thermal, electrical, and nuclear energy.
    • Thermochemistry focuses on the energetic consequences of chemical processes.

    Heat and Work

    • Heat refers to energy flow between objects due to temperature differences, moving from warmer to cooler objects.
    • Work is energy transfer performed by a force moving a mass against resistance.
    • Common work type in chemistry is pressure-volume work (PV-work), illustrated by releasing an inflated balloon.

    Energy Units

    • Joule (J) is the SI unit of energy, defined as ( 1 , \text{J} = 1 , \text{kg m}^2/\text{s}^2 ).
    • Other units include British thermal unit (Btu) and calorie; ( 1 , \text{Btu} = 1055 , \text{J} ), ( 1 , \text{calorie} = 4.184 , \text{J} ).

    Energy Transformation and Conservation

    • Total energy must be conserved during transformations; system + surroundings = universe.
    • Energy flow only occurs as heat (q) and work (w) in defined systems.
    • Change in energy (( \Delta E )) is calculated as ( \Delta E = q + w ).
    • The first law of thermodynamics states that energy can be transformed but not created or destroyed; ( DE_{\text{universe}} = DE_{\text{surroundings}} + DE_{\text{system}} = 0 ).

    Waste Energy

    • Work is commonly extracted from a system by converting heat into work, but not all heat can be efficiently transformed.
    • Waste energy contributes to thermal pollution, altering the normal temperature of bodies of water.
    • Energy conversion efficiency can improve future energy consumption outcomes.

    Heat Capacity and Calorimetry

    • Calorimetry measures heat flow in a system based on three factors: amount of material (m or n), type of material (specific heat capacity ( c ) or molar heat capacity ( C_p )), and temperature change (( \Delta T )).
    • Specific heat capacity describes the heat needed to raise the temperature of one gram of a substance by 1ºC; it varies by compound.

    Enthalpy

    • Enthalpy (( H )) is defined as heat flow under constant pressure, with the change in enthalpy formula: ( \Delta H = \Delta E + P\Delta V ).
    • Exothermic reactions release heat (negative ( \Delta H )); endothermic reactions absorb heat (positive ( \Delta H )).
    • During phase changes, temperature remains constant as thermal energy changes.

    ΔH of Phase Changes

    • Heat of vaporization (( \Delta H_{\text{vap}} )) is the energy required to convert a liquid to a gas (endothermic).
    • Heat of condensation (( \Delta H_{\text{cond}} )) is the energy released converting a gas to a liquid (exothermic).
    • Enthalpy changes are compound-specific and measured in kJ/mol; calculated using ( \Delta H = n \times \Delta H_{\text{phase change}} ).

    Heat and Energy in Reactions

    • Enthalpy changes can be determined for chemical reactions, recognized as heat of reaction.
    • Bond energies provide a way to estimate enthalpy changes; bond breaking requires energy while bond formation releases energy.
    • If more energy is released in bond formation than consumed in bond breaking, the reaction is exothermic.

    Heats of Reaction and Formation

    • Designations for specific reactions include heat of combustion, heat of formation, and heat of neutralization.
    • Standard enthalpy of formation (( \Delta H_f^\circ )) is zero for elements in their standard states.
    • Hess's Law allows calculation of reaction enthalpies through indirect methods when direct measurement is impractical.

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    Test your understanding of molar heat capacity and calorimetry with this quiz. Explore concepts such as heat absorbed calculations and the principles of measuring heat flow. Practical example problems are included to enhance application of the theory.

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