Chemistry Chapter 9: Energy and Chemistry

Questions and Answers

What is considered waste energy in energy conversion?

Heat not converted to work (correct)

Electrical energy

Mechanical energy

Heat used efficiently

What is thermal pollution primarily caused by?

Reduced energy efficiency

Natural seasonal changes

Hot or cold waste streams (correct)

Efficient energy consumption

Which factor does NOT influence the amount of heat absorbed by a system?

The initial temperature (correct)

The temperature change

The mass of the material

The type of material

How is specific heat capacity represented for a substance?

c Signup and view all the answers

What does molar heat capacity indicate?

Heat required for one mole to raise by 1ºC Signup and view all the answers

Which of the following statements is true about specific and molar heat capacities?

Both are compound and phase specific Signup and view all the answers

What is the change in temperature represented by?

ΔT Signup and view all the answers

Which method is used for observing and measuring heat flow into and out of a system?

Calorimetry Signup and view all the answers

What does a nation's energy consumption indicate about its economic status?

It is directly related to economic growth. Signup and view all the answers

What percentage of energy consumption in the US was attributed to the industrial sector in 2011?

31% Signup and view all the answers

What is a significant cause of energy consumption during electricity generation?

Conversion losses Signup and view all the answers

In 2011, what was the total energy supply for the United States in quadrillion Btu?

107.66 quadrillion Btu Signup and view all the answers

Which form of energy accounted for the largest share of energy supply in 2011?

Natural gas Signup and view all the answers

What does the first law of thermodynamics state?

The total energy in a closed system remains constant. Signup and view all the answers

What is the primary use of nearly half of all domestic energy consumption?

Electricity production Signup and view all the answers

Which of the following energy sources accounted for the least portion of the total energy supply in 2011?

Natural gas liquids (NGPL) Signup and view all the answers

What is the sign of ΔH during an endothermic process such as vaporization?

Positive Signup and view all the answers

Which statement accurately describes ΔHcond?

It is an exothermic process. Signup and view all the answers

How is the enthalpy change calculated during a phase change?

ΔH = n x ΔH phase change Signup and view all the answers

What occurs during a phase change with respect to temperature?

Temperature remains constant. Signup and view all the answers

Which phase change is characterized by a positive ΔH value?

Melting of ice Signup and view all the answers

What is the relationship between ΔHvap and ΔHcond?

They are equal in magnitude but opposite in sign. Signup and view all the answers

In the process of heating ice to steam, which calculations are involved?

Both temperature change and phase change enthalpy calculations Signup and view all the answers

What is the unit of measurement for enthalpy changes during phase changes?

kJ/mol Signup and view all the answers

What does Hess's law state about the enthalpy change for a process?

It is independent of the particular way the process is carried out. Signup and view all the answers

What is a characteristic of a state function like enthalpy?

Its value depends only on the current state of the system. Signup and view all the answers

In calculating the enthalpy change using Hess's law, which of these can be considered?

Any convenient pathway between states. Signup and view all the answers

What is the enthalpy change represented by ΔH for the overall combustion of methane?

It is the same for both the direct and stepwise combustion processes. Signup and view all the answers

How is the enthalpy change for a reaction typically calculated using Hess's law?

By applying the formula ΔH = Σ v_i ΔH_f(products) - Σ v_j ΔH_f(reactants). Signup and view all the answers

What does the variable ΔH represent in enthalpy change calculations?

The change in enthalpy for a specified reaction. Signup and view all the answers

Which of the following is true about heat of formation reactions related to Hess's law?

They allow the calculation of enthalpy changes using standard values. Signup and view all the answers

What would be required to find the heat of combustion of propane using Hess's law?

Using tabulated standard enthalpies of formation for CO2 and H2O. Signup and view all the answers

What equation relates the heat flow in a calorimeter to the heat of the reaction?

qreaction = -qcalorimeter Signup and view all the answers

In calorimetry, an increase in temperature can be used to calculate the energy density of a fuel. How is energy density defined?

Energy liberated per gram of fuel burned. Signup and view all the answers

What is the primary difference between qv and qp when discussing the combustion of octane?

qp is measured at constant pressure, while qv is at constant volume. Signup and view all the answers

During an exothermic process, what can be said about ΔH?

ΔH is less than zero. Signup and view all the answers

What happens to the internal energy change (ΔE) in a system during an expansion?

ΔE equals q minus the work done by the system. Signup and view all the answers

Which equation accurately defines the change in enthalpy (ΔH)?

ΔH = DE + D(PV) Signup and view all the answers

For a calorimeter experiment, if the heater supplies 100.0 J of heat with a temperature change of 0.850°C, what can be inferred about the calorimeter's constant?

The calorimeter's heat capacity is 117.65 J/°C. Signup and view all the answers

In the context of a reaction under constant volume, which equation represents the relationship between internal energy change (ΔE) and heat flow (q)?

ΔE = q Signup and view all the answers

Study Notes

Chapter 9: Energy and Chemistry

Economic growth is closely correlated with a nation's energy consumption, represented through Gross Domestic Product (GDP).
In 2011, the United States had an energy supply of 107.66 quadrillion Btu, with significant contributions from coal, natural gas, crude oil, nuclear, and renewable sources.
Domestic production in 2011 accounted for 70.47 quadrillion Btu, while imports contributed 31.02 quadrillion Btu.
Energy consumption distribution in the U.S. was as follows: residential (22%), commercial (19%), industrial (31%), and transportation (28%).
Approximately two-thirds of the energy consumed for electricity generation is wasted due to conversion losses.
Thermal pollution results from waste heat altering the temperature of water bodies, impacting ecosystems.
Calorimetry is the technique used to measure heat flow in chemical reactions, with various dependencies including mass, type of material, and temperature change.
Specific heat capacity (c) measures heat needed to raise 1 gram of a substance by 1ºC; molar heat capacity (Cp) applies to 1 mole of a substance.
The formula for heat energy absorbed is represented as: ( q_{calorimeter} = C_{calorimeter} \times \Delta T_{calorimeter} ) and ( q_{reaction} = -q_{calorimeter} ).

Enthalpy Concepts

Enthalpy (H) is the heat content of a system and is calculated using the relation ( H = E + PV ).
Changes in enthalpy, ( \Delta H ), indicate whether a reaction is exothermic (releases heat, ( \Delta H < 0 )) or endothermic (absorbs heat, ( \Delta H > 0 )).
Phase changes at constant pressure are characterized by enthalpy changes; boiling and freezing involve heat of vaporization (( \Delta H_{vap} )) and heat of condensation (( \Delta H_{cond} )).
( \Delta H ) for phase changes is substance-specific and measured in kJ/mol, calculated using the number of moles involved.

Hess’s Law and Thermodynamic Calculations

Hess's law states the total enthalpy change for a reaction is independent of its pathway; only the initial and final states matter.
Enthalpy changes can be calculated using tabulated data of standard molar enthalpies of formation.
The formula for calculating enthalpy change for a reaction via Hess’s law is: [ \Delta H = \sum v_i \Delta H_f (products) - \sum v_j \Delta H_f (reactants) ]
Practical examples include calculating the heat of combustion for various reactants, demonstrating the application of Hess’s law.

Example Problems

Problems illustrate the use of calorimetry to determine energy density and the enthalpy changes related to phase transitions and chemical reactions, enhancing understanding of thermodynamic principles.

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Description

Explore the relationship between energy consumption and economic growth in this quiz focused on Chapter 9 of Chemistry. Learn about energy sources, consumption distribution in the U.S., and the concepts of calorimetry and thermal pollution. Test your understanding of how energy impact chemical processes and ecosystems.