JAMB CBT Mobile App 2025 - Free Download
JAMB CBT 2025 - Candidates, Schools, Centres, Resellers - Get Ready!

If the heat of combustion of hydrogen is -285.8kJ, What is the heat of formation...

Chemistry
JAMB 2006

If the heat of combustion of hydrogen is -285.8kJ,
What is the heat of formation of water?

  • A. +571.6 kJ
  • B. -571.6 kJ
  • C. -285.8 kJ
  • D. +285.8 kJ
JAMB CBT 2025 - Candidates, Schools, Centres, Resellers - Get Ready!
JAMB CBT Software 2025 - Free Download
JAMB CBT Mobile App 2025 - Free Download
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 127076
Correct Answer: Option C
Explanation

Heat of combustion (ΔH°c) is the energy released when a substance is burnt in oxygen.

The heat of formation (ΔH°f) is the energy released or absorbed when a substance is formed from its constituent elements.

The chemical equation is    H\(_2\)   +  1/2 O\(_2\)  →  H\(_2\)O

Since the heat of formation of H\(_2\)  is zero (ΔHf(H\(_2\) ) = 0 kJ/mol), and the heat of combustion of H\(_2\)  is -285.8 kJ/mol, we can use the following relationship:

ΔHc(H\(_2\) ) = ΔHf( H\(_2\)O) - ΔHf(H\(_2\) )

Rearrange to solve for ΔHf( H\(_2\)O):

 

ΔHf( H\(_2\)O) = ΔHc(H\(_2\) ) + ΔHf(H\(_2\) )

= -285.8 kJ/mol + 0 kJ/mol

= -285.8 kJ/mol

There is an explanation video available below.


Report an Error Ask A Question Download App
JAMB CBT Software 2025 - Free Download
JAMB CBT 2025 - Candidates, Schools, Centres, Resellers - Get Ready!
JAMB CBT Mobile App 2025 - Free Download
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 127076

Explanation Video

JAMB CBT Mobile App 2025 - Free Download
JAMB CBT Software 2025 - Free Download
JAMB CBT 2025 - Candidates, Schools, Centres, Resellers - Get Ready!
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 127076

Contributions ({{ comment_count }})

Please wait...

{{ settings.no_comment_msg ? settings.no_comment_msg : 'There are no comments' }}

Quick Questions

Post your Contribution

Please don't post or ask to join a "Group" or "Whatsapp Group" as a comment. It will be deleted. To join or start a group, please click here

{{ quote.posted_by.display_name }}
{{ settings.form_textarea_description }}
 
JAMB CBT Software 2025 - Free Download
JAMB CBT Mobile App 2025 - Free Download
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 127076
JAMB CBT 2025 - Candidates, Schools, Centres, Resellers - Get Ready!
JAMB CBT Software 2025 - Free Download
JAMB CBT 2025 - Candidates, Schools, Centres, Resellers - Get Ready!
JAMB CBT Mobile App 2025 - Free Download
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 127076