How are the standard enthalpies of an element and a compound determined?

Short Answer

Expert verified
The standard enthalpy of an element in its standard state is always zero by definition and not determined experimentally. The standard enthalpy of a compound is determined experimentally by measuring the heat change when one mole of the compound is formed from its constituent elements in their standard states.

Step by step solution

01

Understanding Enthalpy

Enthalpy is a thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of the system plus the product of pressure and volume.
02

Understanding Standard Conditions

Standard conditions for measuring the enthalpy of an element or a compound refers to the state of a material under specific preset conditions at standard pressure (1 atm) and standard temperature (25 degrees Celsius or 298K). The standard enthalpy is also known as 'enthalpy of formation.', and all elements in their standard states (e.g., O2 gas, H2 gas, etc.) have a standard enthalpy equal to zero.
03

Measuring Enthalpy Changes

Enthalpy changes for elements and compounds are measured using calorimetry. In an experiment, the heat energy transferred in a chemical reaction is used to raise the temperature of water in a calorimeter. By calculating the amount of heat absorbed or released, the change in enthalpy can be determined.
04

Standard Enthalpy of an Element

As all elements in their standard states (e.g. O2 gas, H2 gas, etc.) have a standard enthalpy equal to zero, we don't determine it, it is set by definition.
05

Standard Enthalpy of a Compound

The standard enthalpy of a compound refers to the energy change when 1 mole of a compound is formed directly from its elements in their standard states. For example, the standard enthalpy of formation of Carbon Monoxide (CO) is the enthalpy change when one mole of CO is formed from C in its standard state (solid graphite) and O2 in its standard state (a gas).

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

See all solutions

Recommended explanations on Chemistry Textbooks

View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free