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How is the standard state of an element defined? part A How is the standard state of an element defined? It is the mo...

How is the standard state of an element defined?

part A

How is the standard state of an element defined?

It is the most stable form of an element at 100000 Pa and the specified temperature, usually 0 ∘C.
It is the most stable form of an element at 1 atm and the specified temperature, usually 25 ∘C.
It is the most abundant form of an element.
It is the most stable form of an element at 1 atm and 0 ∘C.

Part B

What is Hess's law?

The total pressure exerted by the mixture of non-reactive gases is equal to the sum of the partial pressures of individual gases.
The overall enthalpy change for a reaction is equal to the sum of the enthalpy changes for the individual steps in the reaction.
The overall energy change for a reaction is equal to the sum of the energy changes for the individual steps in the reaction.
The absolute pressure of a given mass of an ideal gas is inversely proportional to the volume it occupies if the temperature and amount of gas remain unchanged within a closed system.

part C

Why do elements always have ΔH∘f=0?

The internal energy of elements is zero.
ΔH∘ reflects the complexity of compounds.
Elements do not have heteroatomic bonds and these bonds cause enthalpy changes.
The standard state of elements is the reference point for measuring of enthalpy changes.

part D

Write a balanced equation of the combustion of cooking fat.

C51H88O6(l)+70O2(g)→51CO2(g)+44H2O(l)
C51H88O6(l)+70O2(g)→7CO2(g)+44H2CO3(l)
C51H88O6(l)+48O2(g)→51CO2(g)+44H2(g)
C51H88O6(l)+O2(g)→51HCOOH(g)+H2O(l)
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Homework Answers

Answer #1

Ans part A:

It is the most stable form of an element at 1 atm and the specified temperature, usually 25 oC.

Ans part B:

The overall enthalpy change for a reaction is equal to the sum of the enthalpy changes for the individual steps in the reaction.

Ans part C:

The standard state of elements is the reference point for measuring of enthalpy changes

Ans part D:

Standard enthalpy of combustion is defined as the enthalpy change per mole (or per unit amount) of a substance, when it undergoes combustion and all the reactants and products being in their standard states at the specified temperature.

C51H88O6 (l) + 70 O2 (g) -------> 51 CO2 (g) + 44 H2O (l)

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