Thermodynamics: Enthalpy Change and Calorimetry

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Questions and Answers

What is the sign of ∆H for an endothermic reaction?

= 0

< 0

Cannot be determined

> 0 (correct)

What is the term for the heat required to produce 1 mol of a compound from its elements?

Heat of Formation (correct)

Heat of Fusion

Heat of Vaporization

Heat Capacity

What is the unit of specific heat capacity?

J/g°C

J/g.K (correct)

J/mol°C

J/mol.K

A calorimeter is a device used to measure the heat released or absorbed by a _____ process.

physical or chemical Signup and view all the answers

What is the formula to calculate the heat absorbed or released?

q = S x mass x ∆T Signup and view all the answers

What is the specific heat capacity of liquid water?

4.184 J/g.K Signup and view all the answers

What is the primary purpose of a calorimeter?

To measure the heat transfer during a process Signup and view all the answers

What is the specific heat capacity of water in the coffee cup calorimeter experiment?

4.184 J/g°C Signup and view all the answers

What is the formula for the coffee cup calorimeter?

Qsolid = QH2O - msolidCsolid (Tfinal-Tinitial)solid Signup and view all the answers

What is the heat capacity of the calorimeter in the bomb calorimeter experiment?

890 J/°C Signup and view all the answers

What is the enthalpy change for the chemical equation?

The heat of reaction Signup and view all the answers

What type of reaction is the combustion of octane in the bomb calorimeter experiment?

Exothermic reaction Signup and view all the answers

What is the unit of energy that is equivalent to the energy needed to raise the temperature of 1g of water by 1°C?

Calorie (cal) Signup and view all the answers

What is the change in internal energy (∆E) when a system does 451J of work and loses 325J of heat?

126J Signup and view all the answers

In which type of reaction is the change in enthalpy (∆H) approximately equal to the change in internal energy (∆E)?

Reactions involving liquids and solids Signup and view all the answers

What is the term for the heat of reaction, which is the enthalpy change of a reaction?

Enthalpy of reaction (∆H rxn) Signup and view all the answers

What is the characteristic of an endothermic process?

Absorbs heat and results in an increase in enthalpy Signup and view all the answers

Study Notes

Energy and Units

1 calorie (cal) is the energy required to raise the temperature of 1g of water by 1°C
1 kcal = 4.184 kJ
1 kJ = 1000 J = 0.2390 kcal = 239 cal

Internal Energy and Enthalpy

Internal energy (E) is the total energy of a system
Enthalpy (H) is the internal energy plus the product of pressure and volume: H = E + PV
Change in enthalpy (∆H) is the energy plus the product of constant pressure and change in volume: ∆H = ∆E + P∆V

Comparing ∆E and ∆H

For reactions that do not involve gases, ∆H ≈ ∆E
For reactions where the amount of gas does not change, ∆H = ∆E
For reactions where the amount of gas does change, ∆H is very close to ∆E

Exothermic and Endothermic Processes

Exothermic process: releases heat and results in a decrease in the enthalpy of the system (∆H < 0)
Endothermic process: absorbs heat and results in an increase in the enthalpy of the system (∆H > 0)

Enthalpy Changes

Heat of formation (∆Hf): when 1 mol of a compound is produced from its elements
Heat of fusion (∆Hfus): when 1 mol of a substance melts
Heat of vaporization (∆Hvap): when 1 mol of a substance vaporizes

Calorimetry

Heat (q) absorbed by an object is proportional to its temperature change: q = constant × ∆T
Every object has its own heat capacity: Heat Capacity = q/∆T (J/K)
Specific heat capacity (S) is the quantity of heat required to change the temperature of 1 gram of a substance by 1K: S = q/mass × ∆T (J/g.K)

Calculating Heat Absorbed or Released

q = S × mass × ∆T
Molar heat capacity: quantity of heat required to change the temperature of 1 mole of a substance by 1K: Molar Heat Capacity = q/moles × ∆T (J/mol.K)

Types of Calorimetry

Constant-pressure calorimetry: measures heat transfer in a process open to the atmosphere
Constant-volume calorimetry: measures heat transfer in a closed system, such as a bomb calorimeter

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Description

Test your understanding of thermodynamics concepts such as enthalpy change, heat of formation, heat of fusion, and heat of vaporization. This quiz also covers calorimetry and heat capacity.