Video Transcript
What name and symbol are given to
the overall change in energy at constant pressure during a chemical reaction?
To understand the change in energy
during a chemical reaction, let’s look at the combustion of methane as an
example. There are several types of energy
changes that occur during this reaction. The first type of energy involved
in the reaction is chemical potential energy.
Chemical energy is due to the
attraction between particles and their distance from one another. When atoms come together to form
bonds, the chemical energy decreases, which means when atoms are separated, they are
in a higher energy state than when they come together to form molecules. This means that it requires energy
to break the bonds between reactant molecules during a chemical reaction. This increase in energy is absorbed
from the surroundings in the form of thermal energy.
When atoms rearrange to form the
bonds in the product molecules, the chemical potential energy decreases, which is
accompanied by thermal energy being released to the surroundings. The sum of the chemical potential
energy and the thermal energy is the internal energy.
The exact values of the changes in
energy during the reaction are condition dependent. So, depending on the conditions of
the reaction, there are different names and symbols for the internal energy. In chemistry, many reactions occur
at constant pressure. So we consider a form of the
internal energy called the enthalpy, which is given the symbol 𝐻.
So, to sum up, during a chemical
reaction, there are different forms of energy that change. At constant pressure, the total
energy is called the enthalpy, which has the symbol 𝐻. So, to fully answer the question,
the overall change in energy at constant pressure during a chemical reaction would
be the change in enthalpy.
The symbol for the enthalpy change
would be Δ𝐻, because the Δ symbol indicates a change in a quantity. So the name given to the overall
change in energy at constant pressure during a chemical reaction is the enthalpy
change, which has the symbol Δ𝐻.