Measuring Enthalpy Changes in Chemistry
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Questions and Answers

What is the specific heat capacity defined as?

  • The amount of heat needed to raise the temperature of 1 kg of a substance by 1 K (correct)
  • The amount of heat needed to raise the temperature of 1 g of a substance by 1 K
  • The amount of heat released by 1 g of a substance when its temperature decreases by 1 K
  • The amount of heat released by 1 kg of a substance when its temperature decreases by 1 K

    • What is the enthalpy change of reaction?

  • The heat absorbed or released during a physical change
  • The heat absorbed by a substance
  • The heat absorbed or released during a chemical reaction (correct)
  • The heat released by a substance

    • What is the limiting reactant?

  • The reactant that is completely consumed in a reaction (correct)
  • The reactant that is produced in the largest amount
  • The reactant that is present in the largest amount
  • The reactant that has the highest molecular weight

    • Why is the change in temperature measured in calorimetry experiments typically smaller than predicted from theoretical values?

    <p>Due to heat loss from the system (B)</p> Signup and view all the answers

    What is an intensive property?

    <p>A property that does not depend on the amount of substance present (D)</p> Signup and view all the answers

    Which of the following statements accurately describes the relationship between enthalpy change and heat transfer in a chemical reaction?

    <p>Enthalpy change is the heat transferred at constant pressure. (C)</p> Signup and view all the answers

    What is the difference between an endothermic and an exothermic reaction based on energy transfer?

    <p>Endothermic reactions absorb energy from the surroundings, while exothermic reactions release energy into the surroundings. (D)</p> Signup and view all the answers

    Which of the following equations is used to calculate the enthalpy change of a reaction?

    <p>ΔH= −Q/n (C)</p> Signup and view all the answers

    Why does an exothermic reaction result in an increase in temperature?

    <p>The reaction releases heat into the surroundings. (A)</p> Signup and view all the answers

    The standard enthalpy change (ΔH⦵) of a chemical reaction is measured under which conditions?

    <p>Constant pressure and standard temperature. (C)</p> Signup and view all the answers

    What is NOT a form of energy transfer in chemical reactions?

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

    Which of these descriptions accurately defines enthalpy change, ?

    <p>The heat transferred from the system to the surroundings at constant pressure. (B)</p> Signup and view all the answers

    What is the unit for standard enthalpy change, ?

    <p>kJ mol-1 (B)</p> Signup and view all the answers

    In an endothermic reaction, what happens to the heat?

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

    What is the activation energy (Ea) in an energy profile?

    <p>The minimum energy required for the reaction to occur. (C)</p> Signup and view all the answers

    Which of these processes is endothermic?

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

    What is the standard temperature and pressure (STP) used for standard enthalpy change?

    <p>273.15 K and 100 kPa (B)</p> Signup and view all the answers

    What piece of equipment is used to measure the heat exchanged between a system and its surroundings?

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

    In an exothermic reaction, what is the sign of the enthalpy change, ?

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

    What is the role of bond breaking in a chemical reaction?

    <p>Requires energy. (B)</p> Signup and view all the answers

    Study Notes

    Measuring Enthalpy Changes

    • Chemical reactions involve energy transfer between the system and surroundings, conserving total energy.
    • Heat and temperature are different concepts; heat is energy transferred, temperature is a measure of the average kinetic energy of particles.
    • Reactions are classified as endothermic (heat absorbed) or exothermic (heat released) depending on the energy transfer between the system and surroundings.
    • The relative stability of reactants and products determines if a reaction is endothermic or exothermic.
    • Energy profiles show the energy changes during a reaction, with endothermic reactions having a higher energy level for products and exothermic reactions with a lower energy level for products than reactants.
    • Standard enthalpy change (ΔH) is the heat transferred at constant pressure under standard conditions, and is calculated from temperature change of a substance.
    • The equations Q= mcΔT and ΔH = -Q/n are used to calculate enthalpy change. (Q is heat transferred, m is mass, c is specific heat capacity, ΔT is change in temperature, and n is the number of moles).
    • A calorimeter is an apparatus used to measure heat transfer.

    Types of Systems

    • Isolated systems: neither matter nor energy can be exchanged with the surroundings.
    • Closed systems: energy can be exchanged with the surroundings but not matter.
    • Open systems: both matter and energy can be exchanged with the surroundings.

    Heat and Temperature

    • Temperature (T) is a state function, its change is independent of the path.
    • Heat (q) is energy transfer due to a temperature difference; also known as thermal energy.
    • Heat transfer occurs through conduction, convection, and radiation.
    • Heat transfer to an object increases its kinetic energy and can cause a change in temperature or phase change.

    Thermochemistry

    • Thermochemistry is the study of heat changes during chemical reactions.
    • Heat transfer is often described in terms of enthalpy change, which is the heat transferred from a closed system to the surroundings during a chemical reaction.
    • Enthalpy change is measured in kilojoules (kJ).

    Exothermic and Endothermic Reactions

    • Exothermic reactions release heat to the surroundings.
    • Endothermic reactions absorb heat from the surroundings.
    • Bond breaking is an endothermic process.
    • Bond making is an exothermic process.

    Calorimetry

    • Calorimetry is used to determine the enthalpy change of a reaction by measuring the temperature change of a known substance.
    • Measurements can be inaccurate due to heat loss.

    Energy Profiles

    • Activation energy (Ea) is the minimum energy required for a reaction to occur.
    • Energy profiles show the energy changes during a reaction.
    • Exothermic reactions have products at a lower energy level than reactants
    • Endothermic reactions have products at a higher energy level than reactants.

    Standard Enthalpy Change

    • The Plimsoll symbol (273.15 K and 100 kPa) denotes standard temperature and pressure.
    • Standard ambient temperature and pressure (SATP) is 298.15 K and 100 kPa.
    • Standard enthalpy change (ΔH°) refers to the heat transferred at constant pressure under standard conditions and states.
    • Calculations involve heat capacity (c,) which describes how much heat to change the temperature of a substance, by 1 K or 1˚C.
    • Calculations involve the equation Q = mcΔT where Q is the heat transferred, m is the mass, c is the specific heat capacity, and ΔT is the change in temperature

    Practice Questions and Worked Examples

    • Various practice questions and worked examples are provided to demonstrate practical application of the concepts.
    • Key definitions of specific heat capacity, limiting reactant, etc., is used for accurate calculations.

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    Related Documents

    SL R1.1 Measuring Enthalpy Changes PDF

    Description

    This quiz explores the concepts of enthalpy changes in chemical reactions, focusing on the differences between endothermic and exothermic reactions. It covers the principles of energy transfer, how to measure heat under standard conditions, and the relevant equations used in enthalpy calculations.

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