Chemistry Solutions and Thermodynamics Quiz

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Questions and Answers

What is the formula for calculating the molality of a solution?

  • molality = moles of solute/mass of solvent (in kg) (correct)
  • molality = moles of solvent/mass of solute (in kg)
  • molality = mass of solute/moles of solvent (in kg)
  • molality = mass of solvent/moles of solute (in kg)

What is the correct formula for calculating the boiling point elevation (∆Tb) of a solution?

  • ∆Tb = molality / Kb
  • ∆Tb = molality + Kb
  • ∆Tb = Kb * molality (correct)
  • ∆Tb = Kb / molality

What is the molality of the sucrose solution described in the text?

  • 0.514 mol sucrose/kg water
  • 4.39 mol sucrose/kg water (correct)
  • 342 g sucrose/kg water
  • 1500 g sucrose/kg water

What is the boiling point elevation constant (Kb) for water?

<p>0.514 K/mol*Kg (A)</p> Signup and view all the answers

What is the difference between the freezing point of pure solvent and the freezing point of the solution called?

<p>Freezing point depression (D)</p> Signup and view all the answers

Why does the vapor pressure of a solution decrease compared to the pure solvent?

<p>The solute molecules reduce the energy of the solvent molecules, making it harder for them to escape into the vapor phase. (A)</p> Signup and view all the answers

What is the main reason why a solution freezes at a lower temperature than the pure solvent?

<p>The solute molecules decrease the vapor pressure of the solution. (A)</p> Signup and view all the answers

What is the freezing-point depression (∆Tf) defined as?

<p>The freezing point of the pure solvent minus the freezing point of the solution. (A)</p> Signup and view all the answers

What is the formula for calculating work done by a gas during expansion?

<p>W = - P(∆V) (B)</p> Signup and view all the answers

If a gas expands against a vacuum, what is the work done?

<p>The work done is zero. (D)</p> Signup and view all the answers

What is the relationship between work and internal energy?

<p>The relationship between work and internal energy is complex and not easily defined. (C)</p> Signup and view all the answers

How can the internal energy of a system be increased?

<p>Both A and B. (D)</p> Signup and view all the answers

What is the conversion factor between L*atm and Joules?

<p>1 L*atm = 101.3 J (C)</p> Signup and view all the answers

What is the sign convention for work done by a system?

<p>Work done by a system is always negative. (A)</p> Signup and view all the answers

What is heat, in the context of thermodynamics?

<p>The transfer of energy due to a temperature difference. (D)</p> Signup and view all the answers

Which of the following examples demonstrates a situation where heat is added to a system without doing any work?

<p>Heating water in a pot on a stove. (A)</p> Signup and view all the answers

What is the equation used to calculate the molality of the naphthalene solution?

<p>$m = \frac{\Delta Tb}{Kb}$ (B)</p> Signup and view all the answers

What is the mass of the solvent in the solution used to calculate the molar mass of naphthalene?

<p>0.1 kg (B)</p> Signup and view all the answers

What is the molar mass of naphthalene determined in the example?

<p>128 g/mol (B)</p> Signup and view all the answers

What value is commonly used as the boiling point of benzene?

<p>80.1 °C (D)</p> Signup and view all the answers

What is the primary reason for using the equation \Delta Tb = Kbm in this example?

<p>To determine the molality of the naphthalene solution (A)</p> Signup and view all the answers

Why is the boiling point elevation (\Delta Tb) considered a colligative property?

<p>It depends on the number of solute particles in solution (A)</p> Signup and view all the answers

Which of the following is NOT a colligative property?

<p>Heat of vaporization (A)</p> Signup and view all the answers

What is the correct value for the molality of the naphthalene solution calculated in the example?

<p>0.020 mol/kg (D)</p> Signup and view all the answers

What is the van't Hoff factor (i) for a solution of calcium chloride (CaCl2)?

<p>3 (A)</p> Signup and view all the answers

What is the molality of a solution prepared by dissolving 85.40 g of calcium chloride (CaCl2) in 200 g of water (H2O)?

<p>0.800 mol/kg (C)</p> Signup and view all the answers

What is the freezing point depression of the solution described in the previous question (85.40 g CaCl2 in 200 g H2O)? Assume the freezing point depression constant (Kf) for water is 1.86 °C/m.

<p>-8.19 °C (A)</p> Signup and view all the answers

What is the boiling point elevation of the solution described in the previous question (85.40 g CaCl2 in 200 g H2O)? Assume the boiling point elevation constant (Kb) for water is 0.512 °C/m.

<p>1.23 °C (B)</p> Signup and view all the answers

What is the freezing point of the solution described in the previous questions (85.40 g CaCl2 in 200 g H2O)?

<p>-8.19 °C (B)</p> Signup and view all the answers

Which of the following statements is TRUE about colligative properties?

<p>Colligative properties depend on the concentration of the solute. (B)</p> Signup and view all the answers

What is the relationship between boiling point elevation and the concentration of solute in a solution?

<p>Boiling point elevation is directly proportional to solute concentration. (D)</p> Signup and view all the answers

What is the correct way to calculate the boiling point of a solution?

<p>Tb(solution) = Tb(solvent) + ∆Tb (D)</p> Signup and view all the answers

How does the first law of thermodynamics relate to a chemical reaction occurring in a closed system?

<p>Internal energy change equals the heat added and work done on the system. (B)</p> Signup and view all the answers

Which equation represents freezing point depression?

<p>∆Tf = Kfm (D)</p> Signup and view all the answers

What does the van’t Hoff factor account for when calculating properties of electrolyte solutions?

<p>It reflects the number of particles into which a solute dissociates. (C)</p> Signup and view all the answers

In the given freezing point depression equation, what does Kf represent?

<p>The freezing point depression constant of the solvent. (D)</p> Signup and view all the answers

What must be done for proper concentration determination in a laboratory procedure?

<p>Ensure the flask is labeled with the corresponding solution name. (A)</p> Signup and view all the answers

What is the primary reason why the vapor pressure of a solution is lower than that of the pure solvent?

<p>The solute disrupts the alignment of solvent molecules in the solution. (B)</p> Signup and view all the answers

What is the relationship between heat (Q) and work (W) in a thermodynamic process?

<p>Total internal energy change depends on the sum of Q and W. (B)</p> Signup and view all the answers

During a thermodynamic process, if the heat transfer is 200 Joules and the work done is 300 Joules, what is the change in internal energy?

<p>-100 Joules (C)</p> Signup and view all the answers

If 128 Joules of heat is lost from the gas during a compression that does 462 Joules of work, what is the energy change for this process?

<p>-334 Joules (C)</p> Signup and view all the answers

Which of the following correctly describes enthalpy in thermodynamics?

<p>Enthalpy accounts for heat transfer at constant pressure. (C)</p> Signup and view all the answers

What is Hess's Law primarily used for?

<p>To determine the energy absorbed or released in chemical reactions. (D)</p> Signup and view all the answers

Which of the following statements correctly differentiates heat from temperature?

<p>Heat is a form of energy transfer, while temperature measures the thermal energy of a substance. (B)</p> Signup and view all the answers

Which term describes the energy exchange due to temperature difference?

<p>Heat (C)</p> Signup and view all the answers

What happens to the value of W when the value of Q increases during a thermodynamic process?

<p>W decreases by the same amount as Q increases. (A)</p> Signup and view all the answers

Flashcards

Molar Mass

The mass of one mole of a substance, expressed in g/mol.

Boiling Point Elevation (∆Tb)

The increase in boiling point due to solute presence: ∆Tb = Kb * m.

Molality (m)

Measure of solute concentration: m = moles of solute per kg of solvent.

Freezing Point Depression (∆Tf)

The decrease in freezing point due to solute: ∆Tf = Tf° - Tf.

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Tf°

Freezing point of the pure solvent.

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Tf

Freezing point of the solution.

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Vapor Pressure

The pressure exerted by a vapor in equilibrium with its liquid or solid state.

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Equilibrium in Solutions

State where freezing and melting rates are balanced.

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Colligative Properties

Properties that depend on the number of solute particles in solution, not their nature.

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Van't Hoff Factor (i)

A factor that represents the number of particles an electrolyte produces in solution.

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Electrolytes

Substances that dissociate into ions in solution, impacting colligative properties.

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Nonelectrolytes

Substances that do not dissociate into ions and do not conduct electricity in solution.

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Boiling Point Elevation

The increase in boiling point of a solvent due to solute addition, calculated using ∆Tb = iKbm.

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Freezing Point Depression

The decrease in freezing point of a solvent when a solute is dissolved, calculated using ∆Tf = iKf m.

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Calcium Chloride (CaCl2)

A strong electrolyte that dissociates into three ions: one Ca²⁺ and two Cl⁻.

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Dissociation of Electrolytes

The process where ionic compounds separate into individual ions in solution.

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Mass of Naphthalene

The mass of naphthalene used in the calculation, 250 mg or 0.250 g.

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Mass of Benzene

The mass of benzene used in the solution, which is 100 g.

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Molality Calculation

Formula to find molality: m = ΔTb / Kb.

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Formula Rearranging

Transposing equations to solve for desired variable, like molality.

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Number of Moles of Naphthalene

Calculated as moles = molality × mass of solvent.

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Molar Mass Calculation

Molar mass obtained using the number of moles and mass of substance.

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Molecular Formula of Naphthalene

The chemical formula for naphthalene is C10H8.

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Final Calculation Result

The final molar mass of naphthalene calculated to be 128 g/mol.

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Work (W)

The product of force (F) and distance (d), defined as W=Fxd.

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Mechanical Work

Work defined by compression and expansion of gases, among others.

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Work Equation for Gas Expansion

W = -P(∆V), where ∆V is the change in volume and P is external pressure.

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Change in Volume (∆V)

The difference between final and initial volume, ∆V = Vf - Vi.

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No Work Done in Vacuum

When gas expands against a vacuum, no work is performed: W = 0.

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Work against Constant Pressure

Gas expands against a constant pressure; work is calculated using W = -P(∆V).

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Energy Required to Heat Water

4184 J needed to raise 100 g of water from 20°C to 30°C.

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Heat Transfer Methods

Heat can be gained directly, via work, or a mix of both methods described.

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Boiling Point Elevation Equation

The equation to calculate boiling point elevation: ∆Tb = Kb * m.

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Value of Kb

The boiling point elevation constant is 0.514 K/mol*Kg.

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Boiling Point of Solution

Calculated using the equation: Tb(solution) = Tb(solvent) + ∆Tb.

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Freezing Point Depression Equation

The equation to calculate freezing point depression: ∆Tf = Kf * m.

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Value of Kf

The freezing point depression constant is 1.86 °C*Kg/mol.

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First Law of Thermodynamics

States energy cannot be created or destroyed, only transformed: ∆U = Q + W.

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Enthalpy Definition

A thermodynamic property representing heat content of a system.

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Van't Hoff Factor in Solutions

A factor used in colligative property equations to represent ion production.

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Internal Energy (∆U)

The total energy contained within a system due to both heat and work: ∆U = Q + W.

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Heat (Q)

The energy transferred to or from a system due to temperature difference in a process.

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Thermodynamics Process

A sequence of changes in a system involving heat transfer and work done.

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Hess's Law

A principle stating that the total enthalpy change for a reaction is the sum of the enthalpy changes for individual steps.

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Enthalpy

A measurement of energy in a thermodynamic system, often denoted as H, describing the heat content.

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Change in Enthalpy (∆H)

The difference in enthalpy between the products and reactants of a reaction.

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Difference Between Heat and Temperature

Heat is energy transfer; temperature is a measure of thermal energy intensity.

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Study Notes

General Chemistry 2 - Quarter 3 - Module 3

  • Colligative Properties: Properties of solutions that depend on the number of solute particles, not their identity. These include boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure.

Colligative Properties of Nonelectrolytes and Electrolytes

  • Boiling Point Elevation: The increase in the boiling point of a solution compared to the pure solvent. This happens because the presence of solute particles lowers the vapor pressure of the solution.

  • Freezing Point Depression: The decrease in the freezing point of a solution compared to the pure solvent. The solute particles disrupt the crystal lattice structure of the solvent making it harder for the solvent to solidify.

  • Nonelectrolytes: Substances that do not dissociate into ions when dissolved in a solvent. Colligative properties of nonelectrolytes are influenced directly by the number of solute particles.

  • Electrolytes: Substances that dissociate into ions when dissolved in a solvent. The colligative properties of electrolytes are influenced by the number of ions produced upon dissociation.

Determining Molar Mass from Colligative Properties

  • Molality: The moles of solute per kilogram of solvent. Molality is used in calculations dealing with colligative properties because it is independent of temperature.

  • Boiling and Freezing Point Equations: Used to calculate the boiling point elevation or freezing point depression of a solution.

  • Van't Hoff Factor (i): A factor used to account for the number of particles produced upon the dissociation of an electrolyte. The factor is crucial for correct calculations of electrolytes boiling and freezing points.

First Law of Thermodynamics

  • Thermodynamics: The scientific study of the interconversion of heat and other forms of energy.

  • First Law: Energy cannot be created or destroyed, only transformed. The change in internal energy (∆U) of a system equals the heat (Q) added to the system plus the work (W) done on the system. (∆U = Q + W)

  • Work (W): Force applied over a distance (W = F • d). In thermodynamics, work is often associated with expansion or compression of gases.

  • Heat (Q): Energy transferred between a system and its surroundings due to a temperature difference. Positive Q means heat is added to the system; negative Q means heat is lost by the system.

Enthalpy and Hess' Law

  • Enthalpy (H): A thermodynamic potential that is a measure of the system's total heat content. Enthalpy is particularly useful when experiments occur at constant pressure. (H = U + PV)

  • Hess's Law: The overall enthalpy change for a reaction is independent of the pathway. This means the enthalpy change for a reaction can be calculated by summing the enthalpy changes of a series of reactions that add up to the overall reaction,

  • Enthalpy of Reaction (ΔH): The enthalpy change in a chemical reaction.

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