How to find temperature change in entropy and enthalpy?
Answers
Answered by
0
note: delta is represented by a triangle. i just can't type it in a triangle from the keyboard characters so i'm just going to write out 'delta'
------------------------
ENTHALPHY (delta H): the heat content of a chemical. it is basically the difference in heat content of the products and reactants
when delta H (for enthalphy) is NEGATIVE, the reaction is spontaneous.
how to find it:
delta H = (sum of products) - (sum of reactants)
Here's an example problem:
Calculate the heat of combustion of CH4. The heats of formation are as follows:
delta H of CH4 = -74.8 kJ mol
delta H of CO2 = -110.5 kJ mol
delta H of H2O = -241.8 kJ mol
eq: CH4 + 2 O2 --> CO2 + 2 H2O
solution:
delta H = [(CO2)(1) + (H20)(2)] - [(CH4)(1) + (O2)(0)]
= [(-110.5)(1) + (-241.8 )(2)] - [(-74.8)(1) + (0)(2)]
= -519.3 kJ (the rxn is spontaneous since it's negative)
(you multiply the values of each product or reactant by the coefficient. look at H20. it has a coefficient of 2 in the equestion. so take the value they gave you for water, which is -241.8, and multiply it by two. it's that simple. remeber: FOR ENTHALPHY, ELEMENTS DO NOT HAVE A VALUE SO THEY JUST BECOME ZERO. look how the value for oxygen gas was calculated)
------------------------
ENTROPY (delta S): A measure of the disorder or randomness in a closed system.
You do the same process as you did for enthalpy to find entropy. The only difference is that:
when delta S (for entropy) is POSITIVE, the reaction is spontaneos.
AND UNLIKE ENTHALPHY, ELEMENTS DO HAVE VALUES.
your teacher should give you two different charts with the values of enthalpy and entropy. in problems, they usually give you the values within the question so you wouldn't need your chart...
------------------------
They are related to each other when finding GIBBS FREE-ENERGY, or delta G, which is the maximum amount of energy available from any chemical reaction.
equation:
delta G = delta H - Tdelta S
*the T stands for temperature (298K)
once you delta S, multiply that value with the temperature and just subtract that from delta H to find delta G.
if delta G is NEGATIVE, then the reaction is spontaneous.
:)
------------------------
ENTHALPHY (delta H): the heat content of a chemical. it is basically the difference in heat content of the products and reactants
when delta H (for enthalphy) is NEGATIVE, the reaction is spontaneous.
how to find it:
delta H = (sum of products) - (sum of reactants)
Here's an example problem:
Calculate the heat of combustion of CH4. The heats of formation are as follows:
delta H of CH4 = -74.8 kJ mol
delta H of CO2 = -110.5 kJ mol
delta H of H2O = -241.8 kJ mol
eq: CH4 + 2 O2 --> CO2 + 2 H2O
solution:
delta H = [(CO2)(1) + (H20)(2)] - [(CH4)(1) + (O2)(0)]
= [(-110.5)(1) + (-241.8 )(2)] - [(-74.8)(1) + (0)(2)]
= -519.3 kJ (the rxn is spontaneous since it's negative)
(you multiply the values of each product or reactant by the coefficient. look at H20. it has a coefficient of 2 in the equestion. so take the value they gave you for water, which is -241.8, and multiply it by two. it's that simple. remeber: FOR ENTHALPHY, ELEMENTS DO NOT HAVE A VALUE SO THEY JUST BECOME ZERO. look how the value for oxygen gas was calculated)
------------------------
ENTROPY (delta S): A measure of the disorder or randomness in a closed system.
You do the same process as you did for enthalpy to find entropy. The only difference is that:
when delta S (for entropy) is POSITIVE, the reaction is spontaneos.
AND UNLIKE ENTHALPHY, ELEMENTS DO HAVE VALUES.
your teacher should give you two different charts with the values of enthalpy and entropy. in problems, they usually give you the values within the question so you wouldn't need your chart...
------------------------
They are related to each other when finding GIBBS FREE-ENERGY, or delta G, which is the maximum amount of energy available from any chemical reaction.
equation:
delta G = delta H - Tdelta S
*the T stands for temperature (298K)
once you delta S, multiply that value with the temperature and just subtract that from delta H to find delta G.
if delta G is NEGATIVE, then the reaction is spontaneous.
:)
Similar questions