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Author: Subject: Enthalpy Changes
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[*] posted on 7-2-2015 at 05:58
Enthalpy Changes

Somehow during chemistry I started to space out during our lessons on enthalpy, I'm wonder if someone can explain it to me.

What are the values in the CRC book for enthalpies

what is enthalpy of combustion

what is enthalpy of formation

what is heat of formation

what is the lower phase called, before it goes into monoatomic gas phase atoms, and what is the phase called when it comes back to the bottom? this is an addition and subtraction type problem and is used to determine how much energy is given off by a reaction (though sometimes they do fractions of reactions and this is additionally confusing to me)

can someone please help me out, I want to understand the terminology and basics, something got me confused, would really like to learn it. And how can you tell how much energy is released from certain chemical reactions

[Edited on 7-2-2015 by Yttrium2]

[Edited on 7-2-2015 by Yttrium2]
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[*] posted on 7-2-2015 at 10:20

The terms 'heat' and 'Enthalpy' are mostly used interchangeably.

The heat of combusion is the amount of heat released when 1 mol of a substance is fully reacted with oxygen. Example: the heat of combustion of methane is the heat that is released by:

CH4(g) + 2 O2(g) ===> CO2(g) + 2 H2O(l)

The heat of formation of methane is the heat released by:

C(s) + 2 H2(g) === > CH4(g) (formation of a compound from its constituent chemical elements)

Enthalpies of reactions are always expressed as ΔH = H<sub>2</sub> - H<sub>1</sub>, enthalpy of end state (2) minus enthalpy of initial state (1). If enthalpy is released (exothermic reaction), then ΔH < 0 (negative).

[Edited on 7-2-2015 by blogfast25]

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