Penentuan Entalpi Reaksi Berdasarkan Entalpi Pembentukan Standar | Kimia SMA | Tetty Afianti

Summary

In this video, the instructor teaches how to determine reaction enthalpy based on standard enthalpy of formation (ΔHf) and applies Hess's Law. The process involves using formulas to calculate enthalpy changes for reactions, including combustion. Several examples are provided, such as the combustion of propane and acetylene, with detailed calculations and steps. The video explains the importance of balancing chemical equations and using known enthalpies to compute the energy released or absorbed during reactions. Viewers are encouraged to practice with provided exercises and visit a blog for additional learning resources.

Takeaways

• 😀 The script introduces Hess's Law, which states that enthalpy change is independent of the number of steps in a reaction, depending only on the initial and final states of the reaction.
• 😀 The formula for calculating reaction enthalpy (ΔH_reaction) is based on the difference in standard enthalpy of formation (ΔH_f) of the products and reactants.
• 😀 The example problem demonstrates how to calculate the enthalpy change for the combustion of propane (C3H8), using the enthalpies of formation of CO2, H2O, and C3H8.
• 😀 When balancing combustion reactions, the coefficient of the substance being combusted (like propane) remains 1, while the coefficients of the other substances are adjusted to balance the atoms of each element.
• 😀 The script provides a step-by-step guide on calculating the enthalpy change of a reaction, including balancing the reaction, using the standard enthalpies of formation, and applying the appropriate formula.
• 😀 In the second example, the enthalpy of formation of acetylene (C2H2) is calculated using the enthalpy of combustion and the enthalpies of formation for CO2 and H2O.
• 😀 It is essential to use the correct stoichiometry when balancing the reaction, ensuring the number of atoms of each element is the same on both sides of the equation.
• 😀 The script also explains the calculation of the enthalpy of combustion for a given mass of a substance, such as 0.56 g of ethene (C2H4), by first converting the mass into moles.
• 😀 When calculating heat released or absorbed in reactions, the heat change (ΔH) is directly proportional to the amount of substance involved in the reaction.
• 😀 The script includes practice problems, encouraging learners to apply the concepts learned, such as calculating the heat released during combustion and determining enthalpy changes from standard formation enthalpies.

Q & A

What is the definition of Hess's Law as discussed in the transcript?

Hess's Law states that the change in enthalpy of a reaction is independent of the pathway between the initial and final states, meaning it only depends on the initial and final conditions of the reactants and products.

How is the enthalpy of a reaction (ΔH) calculated using standard enthalpies of formation?

The enthalpy of a reaction (ΔH) is calculated by subtracting the sum of the standard enthalpies of formation (ΔHf) of the reactants from the sum of the standard enthalpies of formation of the products.

What is the formula for calculating the enthalpy change of a reaction?

The formula is ΔH reaction = Σ(ΔHf products) - Σ(ΔHf reactants), where ΔHf represents the standard enthalpy of formation of the products and reactants.

In the example with propane combustion, how is the reaction balanced?

In the combustion of propane (C3H8), the reaction is balanced by ensuring that the number of carbon atoms, hydrogen atoms, and oxygen atoms on both sides of the equation are equal. The coefficients for CO2 and H2O are adjusted accordingly.

How are the standard enthalpies of formation (ΔHf) for CO2 and H2O used in the calculation?

The standard enthalpies of formation for CO2 and H2O are used to calculate the total enthalpy change for the combustion reaction by multiplying the ΔHf values by the respective coefficients of CO2 and H2O in the balanced equation.

In the second example with acetylene (C2H2), how is the enthalpy of formation (ΔHf) calculated?

The enthalpy of formation for acetylene (C2H2) is calculated by using the known values of ΔHf for CO2 and H2O and applying the Hess's Law to solve for the unknown ΔHf of C2H2 in the combustion reaction.

What is the significance of the negative sign in the enthalpy values in the examples?

The negative sign in enthalpy values indicates that the reaction is exothermic, meaning that heat is released during the reaction.

How is the enthalpy change for the combustion of 0.56 g of ethene (C2H4) determined?

The enthalpy change for the combustion of 0.56 g of ethene is calculated by first converting the mass of ethene into moles, and then multiplying the number of moles by the enthalpy change per mole for the combustion reaction.

In the example with ethene (C2H4), what does the balanced equation for combustion look like?

The balanced combustion reaction for ethene (C2H4) is C2H4 + 3O2 → 2CO2 + 2H2O, where the coefficients ensure the number of atoms of each element is the same on both sides of the equation.

What is the procedure to calculate the heat released during the combustion of 6.72 L of ethane gas (C2H6)?

To calculate the heat released during the combustion of 6.72 L of ethane, first convert the volume of gas to moles using the molar volume at standard conditions (22.4 L/mol), then calculate the heat released by multiplying the moles of ethane by the enthalpy change for the combustion reaction.