The burning of fuels always leads to the release of considerable amounts of energy. An example is the combustion of ethanol, which can be represented by:

The correct answer is alternative (c) "3 mols of 

 when consumed in the reaction release 456 kJ of energy." Let's solve the question step by step: 1. Analyze the provided chemical equation: 

 of -1368 kJ refers to the energy released by the combustion of 1 mol of ethanol (

). 3. Observe that the equation shows that 1 mol of ethanol reacts with 3 mols of oxygen (

) to complete the reaction. 4. Calculate the energy released by 3 mols of 

 in the reaction. Since the total energy released by 1 mol of ethanol is -1368 kJ, and this amount of energy is associated with 3 mols of 

 will be one-third of -1368 kJ. 5. Divide -1368 kJ by 3 to find the energy released by 1 mol of 

 release 3 times -456 kJ, totaling -1368 kJ, which is the total energy released in the combustion of 1 mol of ethanol. 7. Conclude that alternative (c) is correct, as it states that 3 mols of 

 release 456 kJ of energy, which aligns with the calculation. Note that the negative sign in 

 indicates energy is released (exothermic), but in the alternative, the value is presented as positive, common in exam questions to indicate the energy quantity without concern for the energy flow direction.

Consider the complete combustion reaction of methane, CH4, at constant pressure, which releases heat and is represented by the equation: CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l) with ΔH = -802 kJ/mol. Based on the standard enthalpy of formation of CO2 and H2O, which are respectively -393.5 kJ/mol and -285.8 kJ/mol, calculate the enthalpy change of the reaction considering that all products are in the standard state. Consider that the formed water is in the liquid state. Then, identify the type of reaction in terms of heat release or absorption and justify your answer.

A researcher conducts an experiment in a laboratory, investigating the production of ammonia (NH3) from nitrogen (N2) and hydrogen (H2). To carry out this synthesis, he uses the following chemical reaction: N2(g) + 3H2(g) → 2NH3(g), known as the Haber-Bosch Reaction. Knowing that the enthalpy of formation of ammonia is -46.1 kJ/mol and the enthalpies of formation of hydrogen and nitrogen are 0 kJ/mol, as they are substances in the standard state:

Methanol is a fuel used in Formula 1 racing cars. The complete combustion of 64g of this fuel releases:

For centuries, the use of fossil fuels as the main source of fuel has brought several environmental problems. In the search for cleaner energy, Brazil has stood out for its investments in renewable fuels, such as alcohol and biodiesel. In order for these fuels to be used, they need to be energetically advantageous. The combustion reactions of ethanol, , and methane, , the main components of natural gas, at a temperature of , can be represented by these equations: Considering this information, it is correct to state that the mass of ethanol needed to generate the same amount of heat released in the combustion of 1 mol of methane is approximately,

Question bank: Thermochemistry: Enthalpy

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