Thermochemistry Fundamentals Quiz
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Questions and Answers

What type of energy is not associated with the random motion of atoms and molecules?

  • Nuclear energy
  • Potential energy (correct)
  • Thermal energy
  • Chemical energy

Which of the following accurately describes an exothermic process?

  • The system cools down.
  • Energy is released to the surroundings. (correct)
  • Heat is absorbed from the surroundings.
  • Mass is gained by the system.

In a closed system, which of the following exchanges can occur?

  • Only mass exchange
  • Only energy exchange (correct)
  • No exchange at all
  • Mass and energy exchange

What is the primary energy source for Earth?

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

What is the definition of thermochemistry?

<p>The study of heat change in chemical reactions. (A)</p> Signup and view all the answers

What is the primary purpose of a constant-volume calorimeter?

<p>To measure the heat of combustion of a substance (C)</p> Signup and view all the answers

Why is it assumed that no heat is lost to the surroundings in a constant-volume calorimeter?

<p>The design prevents the transfer of heat or mass with the environment (B)</p> Signup and view all the answers

In a constant-pressure calorimeter, which kind of reactions can be measured?

<p>Non-combustion reactions such as acid-base neutralization (C)</p> Signup and view all the answers

What does the equation $q_{sys} = 0$ indicate in a constant-volume calorimeter?

<p>There is a balance between heat gained by the system and heat lost (A)</p> Signup and view all the answers

What is represented by $q_{water} = ms riangle T$?

<p>The heat absorbed by the water based on its mass and temperature change (A)</p> Signup and view all the answers

In the context of calorimetry, what does the symbol $ riangle H$ represent?

<p>The change in enthalpy for a reaction at constant pressure (B)</p> Signup and view all the answers

How is the heat of dilution typically measured?

<p>Using a simple constant-pressure calorimeter (B)</p> Signup and view all the answers

What common household item can be used to construct a crude constant-pressure calorimeter?

<p>Two Styrofoam coffee cups (B)</p> Signup and view all the answers

What is the sign of DH for an endothermic reaction?

<p>DH &gt; 0 (D)</p> Signup and view all the answers

What amount of heat is absorbed when 1 mole of ice melts at 0°C and 1 atm?

<p>6.01 kJ (D)</p> Signup and view all the answers

What happens to the sign of DH when a reaction is reversed?

<p>It changes sign. (B)</p> Signup and view all the answers

How much heat is released from the combustion of 1 mole of methane?

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

How many kilojoules are released when 266 g of P4 burns in air?

<p>6470 kJ (D)</p> Signup and view all the answers

What is the heat change when the specific heat of a substance is multiplied by 2?

<p>It doubles. (B)</p> Signup and view all the answers

What distinguishes the specific heat from heat capacity?

<p>Heat capacity depends on mass. (A)</p> Signup and view all the answers

What must be included in thermochemical equations?

<p>The physical states of all reactants and products. (C)</p> Signup and view all the answers

If a reaction has a DH of -3013 kJ, what does this indicate?

<p>Heat is released by the system. (D)</p> Signup and view all the answers

In the equation H2O (s) + heat -> H2O (l), how is DH expressed?

<p>DH = 6.01 kJ/mol (C)</p> Signup and view all the answers

What is the standard enthalpy of formation for any element in its most stable form?

<p>It is zero. (A)</p> Signup and view all the answers

How is the standard enthalpy of reaction, ΔH°rxn, calculated?

<p>It is the difference between the total enthalpies of products and reactants. (A)</p> Signup and view all the answers

What does Hess's Law state about enthalpy changes?

<p>Enthalpy changes can be added together for reactions in steps. (B)</p> Signup and view all the answers

What is the significance of the standard enthalpy of formation (ΔH0f)?

<p>It serves as a reference point for all enthalpy changes. (C)</p> Signup and view all the answers

For the reaction C(graphite) + O2(g) → CO2(g), what is the ΔHºrxn value?

<p>-393.5 kJ/mol (A)</p> Signup and view all the answers

Which of the following is a correct expression for calculating ΔH°rxn?

<p>ΔH°rxn = [cΔH°f(C) + dΔH°f(D)] - [aΔH°f(A) + bΔH°f(B)] (C)</p> Signup and view all the answers

What is the standard enthalpy of formation (ΔH0f) for O2(g)?

<p>0 kJ/mol (D)</p> Signup and view all the answers

In the reaction CS2(l) + 3O2(g) → CO2(g) + 2SO2(g), what is the reported ΔHrxn value?

<p>-1072 kJ (C)</p> Signup and view all the answers

What does the 'C' represent in the formula qcal = CcalDt?

<p>Specific heat capacity of the calorimeter. (D)</p> Signup and view all the answers

Which substance has a standard enthalpy of formation value of 1.90 kJ/mol?

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

Flashcards

Constant-Volume Calorimeter

A type of calorimeter designed to measure the heat of combustion of a substance at constant volume.

Heat of Combustion

The heat released or absorbed during a reaction at constant volume.

Enthalpy Change (DH)

The change in enthalpy of a reaction.

Constant-Pressure Calorimeter

A device used to measure the heat of reactions at constant pressure, often used for reactions that don't involve combustion.

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Heat of Water (qwater)

The heat absorbed or released by the water in a calorimeter.

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Heat of Bomb (qbomb)

The heat absorbed or released by the calorimeter itself.

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Heat of Reaction (qrxn)

The heat absorbed or released by the reaction happening inside the calorimeter.

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Specific Heat (s)

The energy required to raise the temperature of a substance by one degree.

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Enthalpy change at Constant Pressure (DH)

A measurement of heat absorbed or released in a chemical reaction carried out at constant pressure.

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Standard Enthalpy of Formation (DHf0)

The heat change that occurs when one mole of a compound is formed from its elements in their standard states at a pressure of 1 atm.

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Standard Enthalpy of Reaction (DHrxn0)

The enthalpy change for a reaction carried out under standard conditions (1 atm pressure and 298 K).

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Hess's Law

The enthalpy change for a reaction can be determined indirectly by adding the enthalpy changes of a series of reactions that add up to the overall reaction. This is because enthalpy is a state function.

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Standard Enthalpy of Formation of Elements

Elements in their most stable form at standard conditions have a standard enthalpy of formation of zero.

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Calculating Standard Enthalpy of Reaction from DHf0

The standard enthalpy of a reaction can be calculated from the standard enthalpies of formation of reactants and products. The formula involves subtracting the sum of the enthalpies of formation of reactants from the sum of the enthalpies of formation of products.

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Calculating Heat Change for a Reaction (qrxn)

The heat change for a specific reaction is equal to the negative of the sum of the heat changes for the water and the calorimeter.

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Calorimeter

A device used to measure the heat change in a chemical reaction or physical process. It's designed to minimize heat loss to the surroundings.

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What is energy?

The ability to do work or produce heat.

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What is radiant energy?

The energy associated with the sun, which is the Earth's primary source.

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What is thermal energy?

The energy associated with the random motion of atoms and molecules.

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What is chemical energy?

The energy stored within the bonds of chemical substances.

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What is thermochemistry?

The study of heat changes in chemical reactions.

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Endothermic Reaction

A chemical reaction that absorbs heat from the surroundings, resulting in a positive change in enthalpy (DH > 0).

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Exothermic Reaction

A chemical reaction that releases heat into the surroundings, resulting in a negative change in enthalpy (DH < 0).

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Thermochemical Equation

A chemical equation that includes the enthalpy change (DH) for the reaction under specific conditions.

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Reversing a Thermochemical Equation

The enthalpy change (DH) for a reaction is reversed when the reaction is reversed.

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Scaling a Thermochemical Equation

Multiplying a thermochemical equation by a factor 'n' multiplies the enthalpy change (DH) by the same factor.

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Heat Capacity (C)

The amount of heat required to raise the temperature of a given quantity of a substance by one degree Celsius.

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Heat (q)

The amount of heat absorbed or released by a substance during a temperature change. Calculated by q = m x s x DT or q = C x DT, where m is mass, s is specific heat, C is heat capacity, and DT is the temperature change.

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Extensive Property

A property that depends on the amount of substance present.

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Intensive Property

A property that is independent of the amount of substance present.

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Study Notes

Thermochemistry: Fundamentals

  • Thermochemistry is the study of heat changes in chemical reactions.
  • Energy is the capacity to do work or produce heat.
  • Radiant energy originates from the sun.
  • Thermal energy is associated with the random motion of atoms and molecules.
  • Chemical energy is stored within the bonds of chemical substances.
  • Nuclear energy is stored within the nucleus of an atom.
  • Potential energy is energy available due to an object's position.
  • Energy forms are interchangeable. One form's disappearance necessitates an equal magnitude appearance of another form (Law of Conservation of Energy).

Energy Changes in Chemical Reactions

  • Nearly all chemical reactions either release or absorb energy, often in the form of heat.
  • Thermal energy is related to the movement of atoms and molecules.
  • Heat is the transfer of thermal energy between objects at different temperatures.
  • Temperature measures thermal energy.

System and Surroundings

  • The system is the specific part of the universe being studied.
  • The surroundings are the rest of the universe external to the system.
  • The universe encompasses both the system and its surroundings.

Types of Systems

  • Open systems exchange both mass and energy.
  • Closed systems exchange only energy.
  • Isolated systems exchange neither mass nor energy.

Exothermic and Endothermic Processes

  • Exothermic processes release heat to the surroundings, indicated by a negative enthalpy change (ΔH < 0).
  • Endothermic processes absorb heat from the surroundings, indicated by a positive enthalpy change (ΔH > 0).

Thermodynamics

  • Thermodynamics is the field of chemistry that studies energy and its conversion in physical and chemical processes. It allows predictions about whether a particular process will occur.
  • Thermodynamics analyzes changes in a system using state properties.

State Functions

  • State functions are properties dependent solely on the current state of a system, not the path taken to reach that state. Examples include energy, pressure, volume, and temperature.
  • Changes in state functions are determined by initial and final states.

The First Law of Thermodynamics

  • Energy can be converted but neither created nor destroyed. The total energy of the universe remains constant.
  • The change in a system's internal energy (ΔE) equals the heat exchanged with the surroundings plus/minus the work done on/by the system (ΔE = q + w). Sign conventions apply. (q = heat, w=work)

Work Done by the System

  • Work done by a gas on its surroundings is defined as w = -PΔV.
  • The work done is dependent on pressure and change in volume.

Calorimetry

  • Calorimetry measures heat changes in processes using a calorimeter. Substances respond differently to heat.
  • Specific heat is the amount of heat to raise the temperature of 1g by 1°C.
  • Heat capacity is the amount of heat to increase the temperature of a given mass by 1°C.
  • Heat calculations use q = mcΔT, where q is heat, m is mass, c is specific heat, and ΔT is the temperature change.

Constant-Volume Calorimetry (Bomb Calorimeter)

  • Measure heat of combustion.
  • Compounds are ignited in a pressurized container (bomb) filled with oxygen immerses in water.
  • Heat evolved during combustion increases the temperature of the water.
  • Calibrated device to measure temperature changes to calculate heat of combustion.

Constant-Pressure Calorimetry (Styrofoam Cups)

  • Simpler device for measuring non-combustion reactions.
  • Styrofoam cup is the calorimeter.
  • Heat loss to the surroundings is less of a factor.
  • Useful for measuring heats of neutralization, solution, and dilution.

Enthalpy

  • Enthalpy is a state function that relates to a system's heat content at constant pressure.
  • Standard enthalpy of formation (ΔH°f) is the heat change for forming 1 mole of a compound from its elements in their stable form.

Standard Enthalpy of Reaction

  • Standard enthalpy of reaction is the enthalpy change for a process at constant pressure.

  • Hess's Law states that the enthalpy change for a reaction is the same whether carried out in one step or multiple steps.

  • Enthalpy changes can be calculated using standard enthalpies of formation and the balanced equation of the reaction from the principle, ΔH°rxn = ΣnΔH°f(products) - ΣmΔH°f(reactants).

Other topics mentioned

  • Calculating heat of combustion
  • Heat of solution

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Description

Test your knowledge on the fundamentals of thermochemistry, including the various forms of energy and their transformations during chemical reactions. This quiz covers energy changes, the concept of systems and surroundings, and the Law of Conservation of Energy.

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