CP7 Measuring Enthalpy Changes

• What is enthalpy change defined as?

  Heat released or absorbed
• Enthalpy change is positive for endothermic reactions.
• Exothermic reactions have a negative enthalpy change.
• What is the enthalpy change for the combustion of methane in kJ/mol?

  -890
• Calorimetry is the process of measuring heat changes during a reaction using a device called a calorimeter.
• Steps in a calorimetry experiment

  1️⃣ Prepare the calorimeter by adding reactants

  2️⃣ Record the initial temperature

  3️⃣ Initiate the reaction

  4️⃣ Observe the temperature change

  5️⃣ Calculate the heat absorbed or released
• The formula $q =$$mc\Delta T$ is used to calculate heat changes in calorimetry.
• In the formula $q =$$mc\Delta T$, what does $m$ represent?


  Mass
• If 50g of water increases in temperature by $10^\circ C$, the heat absorbed is 2090 J.
• Enthalpy change is positive for exothermic reactions.

  False
• Match the steps in calorimetry with their descriptions:

  Prepare the calorimeter ↔️ Add reactants to the calorimeter

  Record initial temperature ↔️ Measure the starting temperature of reactants

  Initiate the reaction ↔️ Start the chemical reaction

  Calculate heat change ↔️ Use $q =$$mc\Delta T$
• What is the formula used to calculate heat change in calorimetry?

  $q =$$mc\Delta T$
• In calorimetry, the specific heat capacity of water is 4.18 J/g°C.
• The value of $c$ in $q =$$mc\Delta T$ is the specific heat capacity.
• What formula is used to calculate heat change in calorimetry?

  $q =$$mc\Delta T$
• Calorimetry is the process of measuring heat changes during a chemical reaction or physical transformation using a calorimeter
• Key steps in a calorimetry experiment

  1️⃣ Prepare the calorimeter with reactants

  2️⃣ Record the initial temperature

  3️⃣ Initiate the reaction and observe the temperature change

  4️⃣ Calculate the heat change using $q =$$mc\Delta T$
• In calorimetry, q</latex> represents the heat change.
• What is the heat change when 50g of water with a specific heat capacity of $4.18 \, J / g^\circ C$ increases in temperature by $10^\circ C$?


  $2090 \, J$
• Enthalpy change is measured at constant pressure.
• Enthalpy change ($\Delta H$) is the amount of heat released or absorbed during a chemical reaction at constant pressure
• Match the calorimeter type with its uses:

  Simple Calorimeter ↔️ Reactions in solution at constant pressure

  Bomb Calorimeter ↔️ Reactions at constant volume

  Differential Scanning Calorimeter (DSC) ↔️ Phase transitions, heat capacity changes
• What is the enthalpy change for the combustion of methane?

  $- 890 \, kJ / mol$
• If 50g of water (c = 4.18 \, J / g^\circ C</latex>) increases in temperature by $10^\circ C$ during a reaction, the heat absorbed would be 2090 \, J
• Match the calorimetry step with its description:

  Prepare calorimeter and reactants ↔️ Assemble the calorimeter and add reactants

  Record initial temperature ↔️ Measure the starting temperature of reactants

  Initiate reaction ↔️ Begin the chemical reaction or physical transformation

  Calculate heat change ↔️ Use $q =$$mc\Delta T$ to find heat absorbed or released
• What is the process of measuring heat changes called?

  Calorimetry
• The instrument used in calorimetry to measure heat changes is called a calorimeter
• What are the steps in the calorimetry process?

  1️⃣ Prepare the calorimeter and add reactants

  2️⃣ Record the initial temperature

  3️⃣ Start the reaction

  4️⃣ Calculate the heat change
• The formula $q =$$mc\Delta T$ is used to calculate heat change in calorimetry.
• If 50g of water increases in temperature by 10°C, what is the heat absorbed?

  2090 J
• A simple calorimeter is ideal for reactions in solution at constant pressure
• Match the type of calorimeter with its appropriate use:

  Simple Calorimeter ↔️ Reactions in solution at constant pressure

  Bomb Calorimeter ↔️ Reactions at constant volume

  DSC ↔️ Phase transitions, heat capacity changes
• What type of calorimeter is used for reactions at constant volume?

  Bomb Calorimeter
• A DSC is used to measure small heat changes and automate the process
• Calibrating calorimeters ensures accurate enthalpy change measurements.
• What is used to calibrate a bomb calorimeter?

  Benzoic acid
• What are the steps to perform enthalpy change measurements using a calorimeter?

  1️⃣ Prepare the calorimeter

  2️⃣ Set up the reaction

  3️⃣ Measure temperature changes

  4️⃣ Calculate enthalpy change
• What is the term for the amount of heat released or absorbed during a chemical reaction at constant pressure?

  Enthalpy change
• Enthalpy change is positive for endothermic reactions, indicating heat is absorbed
• Calorimetry measures heat changes during chemical reactions or physical transformations.