2C(s) + 2H2(g) + 52.5 kJ -> C2H4
The enthalpy of formation of carbon disulfide (CS2) can be indicated by the reaction: C(s) + 2 S(s) → CS2(l). This reaction represents the formation of one mole of CS2 from its elements in their standard states. The enthalpy change associated with this reaction is +89.4 kJ/mol, meaning that 89.4 kJ of energy is absorbed when one mole of CS2 is formed from solid carbon and solid sulfur.
The reaction that shows the enthalpy of formation of H2S as -20.6 kJ/mol is: 2H2(g) + S(s) → 2H2S(g) with ΔH = -20.6 kJ/mol. This means that forming 1 mole of H2S from its elements H2 and S releases 20.6 kJ of energy.
The enthalpy of formation (ΔHf) of C2H4 can be determined through the reaction of its constituent elements in their standard states: 2 C(s) + 2 H2(g) → C2H4(g). The enthalpy change for this reaction is measured to be +52.5 kJ/mol, indicating that forming ethylene (C2H4) from graphite (C) and hydrogen gas (H2) requires this amount of energy. This value represents the standard enthalpy of formation for C2H4, defined as the heat absorbed when one mole of a compound is formed from its elements at standard conditions.
The formation of nitrogen dioxide (NO2) from its elemental constituents can be represented by the reaction: N2(g) + 2 O2(g) → 2 NO2(g). The enthalpy change for this reaction indicates that 33.1 kJ/mol of energy is required to form NO2. This value reflects the energy needed to break the bonds in the reactants and form the bonds in the product. Thus, the positive enthalpy change signifies that the reaction is endothermic, necessitating an input of energy for the formation of NO2.
The formation of carbon dioxide (CO2) from its elements can be represented by the reaction: [ C(s) + O_2(g) \rightarrow CO_2(g) ] This reaction is exothermic, meaning it releases energy. The enthalpy change (ΔH) for this reaction is -393.5 kJ/mol, indicating that when one mole of CO2 is formed from carbon and oxygen, 393.5 kJ of energy is released into the surroundings. This release of energy is often measured using calorimetry in a controlled environment.
H2(g) + S(s) H2S + 20.6 kJ
2C(s) + 2H2(g) + 52.5 kJ -> C2H4
C(s) + 2S(s) + 89.4kJ --} CS2(l)
C(s) + 2S(s) + 89.4 kJ --> CS2(l)
The enthalpy of formation (Hf) of H2S at -20.6 kJ/mol indicates that the formation of H2S from its elements (hydrogen and sulfur) is an exothermic reaction. In an energy profile, this would be represented by a diagram showing the reactants at a higher energy level than the products (H2S), with a downward slope indicating the release of energy. Additionally, the activation energy barrier would be visible, representing the energy required to initiate the reaction, but the overall change in energy would reflect the negative enthalpy value.
1/2 N2(g) + O2(g) + 33.1 kJ NO2(g)
The reaction that shows the formation of CO2 releasing 393.5 kJ/mol is typically represented as the combustion of carbon or hydrocarbons. For example, the reaction for the combustion of carbon can be written as: [ C(s) + O_2(g) \rightarrow CO_2(g) ] This reaction indicates that the formation of one mole of carbon dioxide from solid carbon and oxygen gas releases 393.5 kJ of energy, demonstrating an exothermic process.