Chemistry Chapter on Ideal Gas Expansion

Questions and Answers

Under what conditions is the relation ∆H = ∆E + P∆V valid for a system?

Constant temperature, pressure and composition

Constant temperature

Constant pressure

Constant temperature and pressure (correct)

What happens to the enthalpy change (∆H) during the complete isothermal expansion of an ideal gas?

May be positive or negative (correct)

Always negative

Always positive

Zero

For the reaction 2C6H6(l) + 15O2(g) → 12CO2(g) + 6H2O(l), what is indicated by the difference between heats of reaction at constant pressure and constant volume?

It is equal to zero

It indicates a negative value

It varies depending on the reaction conditions

It results in a positive value (correct)

For the reversible isothermal expansion of one mole of an ideal gas at 300 K from a volume of 10 dm³ to 20 dm³, what is ∆H?

Zero Signup and view all the answers

Given that for the reaction CaCO3(s) → CaO(s) + CO2(g) at 977°C, ∆H = 174 kJ/mol, what is the approximate value of ∆E?

163.6 kJ Signup and view all the answers

What is the heat of combustion of C2H6 in kCal/mol?

-1349 kCal/mol Signup and view all the answers

If 3 g of graphite is burnt in excess oxygen, which of the following represents the quantity of heat liberated when considering the heat of formation of CO2?

94.0 kCal Signup and view all the answers

Which value represents the heat change for the reaction C2H2 + H2 → C2H4?

-41.8 kCal Signup and view all the answers

What is the heat of hydrogenation of ethene based on the provided heats of combustion?

-136.8 kJ Signup and view all the answers

Which statement is true regarding the heat of combustion of substances?

It can be both positive and negative. Signup and view all the answers

What is the daily consumption of sugar if the heat of combustion is -1349 kCal/mol?

728 g Signup and view all the answers

Which is the correct heat of combustion for C2H4?

-363.7 kCal Signup and view all the answers

Which of the following values corresponds to an endothermic reaction based on combustion data?

+1.368 kJ Signup and view all the answers

What is the heat of combustion when one mole of graphite burns?

–128.02 kJ mole Signup and view all the answers

Which is the enthalpy of formation for CH4 based on the given combustion values?

–18.4 K Cal Signup and view all the answers

What is standard enthalpy of formation for C(s) at 25 °C?

0 kJ/mol Signup and view all the answers

What is the enthalpy of combustion of C2H4?

–1412 kJ mole–1 Signup and view all the answers

What is the enthalpy of combustion of one mole of benzene?

3267.0 kJ Signup and view all the answers

What enthalpy value corresponds to the combustion of 0.4 g of CH4?

0.25 kCal Signup and view all the answers

At what pressure is the enthalpy of formation for C2H4(g), CO2(g), and H2O(l) measured?

1 atm Signup and view all the answers

Which of the following species has a standard enthalpy of formation of zero?

Br(g) Signup and view all the answers

What is the standard enthalpy of formation of 1 mole of water vapor at 25°C in kCal?

-78.84 kCal Signup and view all the answers

Which of the following expressions correctly relates to the enthalpy of formation of carbon monoxide?

∆ H0f (CO,g) = ∆ H0f (CO2,g) - ∆ H0f (O2,g) Signup and view all the answers

What is the enthalpy change (∆H) for the combustion of 5 moles of acetylene?

-1310 kJ Signup and view all the answers

In the formation of 2 moles of CO2 and water from acetylene and oxygen, what is the sign of ∆H?

Negative Signup and view all the answers

Which of the following statements regarding the enthalpy of formation is false?

Enthalpy of formation is independent of the reaction conditions. Signup and view all the answers

What would happen to the enthalpy of formation of acetylene if the temperature decreased significantly?

It would decrease. Signup and view all the answers

Which of the following is the correct enthalpy of formation for acetylene?

-1802 kJ Signup and view all the answers

What is the enthalpy change for the formation of 1 mole of carbon dioxide?

-393.5 kJ Signup and view all the answers

What is the value of ∆G for a spontaneous reaction when T > 425 K?

-2.7 kCal Signup and view all the answers

Which equation correctly represents the relationship of Gibbs free energy change in a reversible process?

∆G = –2.30 RT log K Signup and view all the answers

What is the change in internal energy ∆U of the gas after expanding against a constant external pressure of 2.5 atm, given the initial and final volumes?

-505 J Signup and view all the answers

What is the heat exchange in the formation of 35.2 g of CO2 from carbon and oxygen gas, if the enthalpy of combustion is -393.5 kJ/mol?

-315 kJ Signup and view all the answers

Given the bond dissociation enthalpies of X2, Y2, and XY in a ratio of 1 : 0.5 : 1, what is the ∆H for the formation of XY if it is -200 kJ/mol?

-200 kJ Signup and view all the answers

At what temperature range will ∆G be greater than 0 for the reaction in question?

T < 425 K Signup and view all the answers

In which scenario is ∆G equal to 0?

At equilibrium Signup and view all the answers

How is the value of ∆G influenced by changes in temperature for a spontaneous reaction?

Varies but is always negative Signup and view all the answers

Study Notes

Gaseous Reactions and Enthalpy Changes

Complete isothermal expansion of an ideal gas can result in negative, positive, zero, or varying ∆H values.
For isothermal expansion of one mole of an ideal gas from 10 dm³ to 20 dm³, ∆H is given as either +1.73 kJ or -1.73 kJ.
Reaction CaCO3(s) → CaO(s) + CO2(g) at 977°C has ∆H = 174 kJ/mol, while ∆E varies depending on specific conditions including volume and temperature.

Heat of Reaction

Heats of reaction differ between constant pressure and constant volume, illustrated by the example 2C6H6(l) + 15O2(g) → 12CO2(g) + 6H2O(l).
The heat of combustion for a specific reaction involving CO and O2 is noted as -67.71 kcal at 17°C.
Combustion of one mole of graphite releases values around -394 kJ to -504 kJ.

Enthalpy of Formation

Enthalpy of combustion for CH4, C(s), and H2(g) at 25 °C are -212.4 kcal, -94.0 kcal, and -68.4 kcal respectively.
Enthalpy of formation for CH4 is expressed as a positive value, calculated through its combustion data.

Standard Enthalpy Values

Standard enthalpy of formation is zero for elements in their most stable forms (e.g., Cgraphite, Br(g)).
Combustion of benzene generates considerable heat (3267.0 kJ), affecting caloric intake calculations for daily sugar consumption.

Heat of Formation and Combustion

The heat of formation of C2H4 and subsequent reactions leads to calculated enthalpies for various products, emphasizing bond strength variations.
The reaction enthalpy of the formation of CO(g) from C and O₂ provides insights into various thermodynamic equations and relationships.

Relationships in Thermodynamics

The expression ∆H = ∆E + P∆V holds under constant temperature and pressure.
Correct equations for the relationship between enthalpy and Gibbs free energy are essential for understanding system behavior in equilibrium.

Key Concepts in Heat Transfer

Heat transfer in reactions varies widely; for example, combustion reactions may absorb or release significant amounts of heat under specific conditions.
For example, the dissociation enthalpies and formation enthalpies are critical data points for predicting reaction outcomes.

Application in Analytical Chemistry

A methodical approach to reaction enthalpy and energy changes enhances understanding of chemical processes, stability, and spontaneous reactions.

Solid-State Reactions

The enthalpy changes involved in solid-state reactions, such as the breakdown of CaCO3, highlight the importance of temperature and pressure constraints in calculating energy changes.

Final Note

Overall, a comprehensive understanding of enthalpy and energetic relationships is crucial for analyzing chemical reactions and their feasibility in experimental and industrial processes.

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Description

This quiz examines the principles of isothermal expansion of ideal gases and analyzes the combustion of isobutane. Participants will explore the relationships between enthalpy and internal energy in gaseous reactions. Test your understanding of thermodynamics with this focused quiz.