important points on bond enthalpy for quick revision. if possible write in notebook!
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Answer:
energy. Quantifying the energy represented by the bonds in different molecules is an important part of understanding the overall energy implications of a reaction. In this article, we'll explore two different concepts that help describe that energy: enthalpy of reaction and bond enthalpy.
Enthalpy of reaction
During chemical reactions, the bonds between atoms may break, reform or both to either absorb or release energy. The result is a change to the potential energy of the system. The heat absorbed or released from a system under constant pressure is known as enthalpy, and the change in enthalpy that results from a chemical reaction is the enthalpy of reaction. The enthalpy of reaction is often written as \Delta\text H_{\text{rxn}}ΔH
rxn
delta, start text, H, end text, start subscript, start text, r, x, n, end text, end subscript.
To better understand enthalpy of reaction, let's consider the hydrogenation of propene, \text{C}_3 \text{H}_6C
3
H
6
start text, C, end text, start subscript, 3, end subscript, start text, H, end text, start subscript, 6, end subscript, to form propane, \text{C}_3 \text{H}_8C
3
H
8
start text, C, end text, start subscript, 3, end subscript, start text, H, end text, start subscript, 8, end subscript. In this reaction, propene gas reacts with hydrogen gas, \text H_2(g)H
2
(g)start text, H, end text, start subscript, 2, end subscript, left parenthesis, g, right parenthesis, to form propane gas:
~~~~~~~\text{C}_3 \text{H}_6(g)~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~ \text H_2(g) ~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text{C}_3 \text H_8 (g)