Textbook Question
Write balanced equations that describe the formation of the following compounds from elements in their standard states, and then look up the standard enthalpy of formation for each substance in Appendix C: (a) NH4NO3(s)
8. Thermochemistry
Formation Equations
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Which of the following is the correct formation equation for NO2(g) from its elements in their standard states?
A
N2(g) + 2O2(g) → 2NO2(g)
B
N2(g) + O2(g) → NO2(g)
C
1/2N2(g) + O2(g) → NO2(g)
D
N2(g) + O2(g) → 2NO2(g)
Verified step by step guidance1
Understand the concept of a formation equation: A formation equation represents the formation of one mole of a compound from its elements in their standard states.
Identify the elements involved: For NO2(g), the elements are nitrogen (N) and oxygen (O). In their standard states, nitrogen is N2(g) and oxygen is O2(g).
Determine the stoichiometry: The formation equation should produce exactly one mole of NO2(g). Therefore, the coefficients of the reactants must be adjusted to reflect this.
Balance the equation: Since NO2 contains one nitrogen atom and two oxygen atoms, start by balancing nitrogen. Use 1/2 mole of N2(g) to provide one nitrogen atom. Then, use one mole of O2(g) to provide the two oxygen atoms needed.
Write the balanced formation equation: The correct formation equation is 1/2N2(g) + O2(g) → NO2(g), ensuring that the equation reflects the formation of one mole of NO2(g) from its elements in their standard states.
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