🧪 CÁLCULO DA VARIAÇÃO DA ENTALPIA: CALOR DE FORMAÇÃO

Summary

In this engaging video, the presenter, Gabriel Cabral, teaches how to calculate the enthalpy change (ΔH) of a reaction using heat of formation values. He explains key concepts like the zero value of heat formation for simple substances and how to use a formula to subtract the sum of reactants' enthalpies from the sum of products' enthalpies. With a clear example of ethanol combustion, Cabral walks through each step of the process, helping viewers easily grasp the concept of calculating ΔH. The video encourages interactive learning and emphasizes the importance of practice and consistency in mastering chemical calculations.

Takeaways

• 😀 Heat of formation is the enthalpy change when one mole of a compound is formed from its elements in their most stable state.
• 😀 The heat of formation for simple substances like O₂, N₂, and H₂ is zero.
• 😀 To calculate delta H, use the formula: ΔH = Σ (Enthalpies of products) - Σ (Enthalpies of reactants).
• 😀 You subtract the sum of the enthalpies of the reactants from the sum of the enthalpies of the products.
• 😀 Example: In the combustion of ethanol, the sum of enthalpies of products is -1,645 kJ/mol, and reactants is -277.8 kJ/mol.
• 😀 To calculate delta H, use the heat of formation values for each substance involved in the reaction.
• 😀 For CO₂, the heat of formation is -393.5 kJ/mol, and for H₂O, it's -285.6 kJ/mol.
• 😀 When calculating, remember to multiply the heat of formation by the number of moles involved in the reaction.
• 😀 For the combustion of ethanol, after calculations, delta H comes out to be -1,367.2 kJ/mol.
• 😀 Professor Cabral encourages viewers to use this method in their future chemistry problems and promotes his platform for further learning.

Q & A

What is the main topic of the video?

The main topic of the video is teaching how to calculate the change in enthalpy (ΔH) of a reaction using the heat of formation values of substances involved.

What does the host mean by 'heat of formation'?

Heat of formation refers to the heat change when one mole of a compound is formed from its elements in their standard states under standard conditions.

What is the significance of the heat of formation being zero for certain substances?

Substances in their most stable, elemental forms, such as O2, N2, and H2, have a heat of formation of zero because no energy is required to form them from their elements in their standard states.

What is the basic formula for calculating ΔH using heat of formation?

The formula for calculating ΔH is: ΔH = (sum of enthalpies of products) - (sum of enthalpies of reactants).

How does the host suggest using the reaction equation for calculation?

The host suggests writing the enthalpy values for each substance in the reaction, then summing the enthalpies of the products and subtracting the sum of the enthalpies of the reactants.

Why is the heat of formation of O2 not provided in the example?

The heat of formation of O2 is not provided because O2 is a simple elemental substance, and its heat of formation is zero by definition.

What values are used in the example to calculate ΔH for the combustion of ethanol?

The values used are the heat of formation of CO2 (-393.5 kJ/mol), H2O (-285.9 kJ/mol), and ethanol (-277.8 kJ/mol), as well as the stoichiometric coefficients of each substance in the reaction.

What is the importance of the minus sign in the heat of formation values?

The minus sign indicates that the formation of these substances from their elements releases energy, making them exothermic reactions.

How does the host ensure that the correct enthalpy values are applied to the right side of the reaction?

The host ensures this by placing the appropriate heat of formation values next to each substance in the reaction, with products on the right side and reactants on the left side.

What is the final result for ΔH in the example of ethanol combustion?

The final result for ΔH is -1367.2 kJ, which means the combustion of ethanol releases this amount of heat energy.