Termokimia (4) | Menentukan ∆H Reaksi Berdasarkan

Summary

In this educational video on thermochemistry, the presenter explains how to determine the enthalpy change (delta H) of chemical reactions using standard enthalpy of formation data (delta Hf). Through examples, such as the formation of water and carbon dioxide, viewers learn to calculate delta H by subtracting the total delta Hf of reactants from that of products. The video also includes detailed calculations for specific reactions, providing a clear understanding of how to apply these concepts in real-world scenarios.

Takeaways

• 😀 Thermochemistry studies the heat changes during chemical reactions, particularly the enthalpy change (ΔH).
• 😀 Standard enthalpy of formation (ΔH_f) represents the heat absorbed or released when one mole of a compound forms from its elements.
• 😀 A compound's ΔH_f value indicates how much heat is released (negative value) or absorbed (positive value) during formation.
• 😀 Elements in their standard state have an enthalpy of formation (ΔH_f) value of zero.
• 😀 To calculate the enthalpy change of a reaction, subtract the total ΔH_f values of the reactants from the total ΔH_f values of the products.
• 😀 For example, the formation of water (H2O) releases 242 kJ/mol, indicating it is an exothermic reaction.
• 😀 In a reaction with multiple compounds, remember to multiply the ΔH_f values by their respective coefficients in the balanced equation.
• 😀 When calculating ΔH for a reaction, ensure to use the correct values for both products and reactants.
• 😀 If calculating the ΔH for combustion reactions, convert grams of reactants to moles using molar mass.
• 😀 The final ΔH value for a reaction can be scaled based on the number of moles of the substance being considered.

Q & A

What is thermochemistry?

Thermochemistry is a branch of chemistry that studies the heat involved in chemical reactions, particularly the changes in enthalpy (ΔH).

What does ΔH represent in a chemical reaction?

ΔH represents the change in enthalpy, indicating the amount of heat absorbed or released during a reaction.

What is the standard enthalpy of formation (ΔHf)?

The standard enthalpy of formation (ΔHf) is the amount of heat change when one mole of a compound is formed from its elements in their standard states.

What is the ΔHf value for H2O?

The ΔHf value for H2O is -242 kJ/mol, indicating that heat is released when one mole of water is formed.

How is the ΔH of a reaction calculated?

The ΔH of a reaction is calculated using the formula ΔH = (sum of ΔHf of products) - (sum of ΔHf of reactants).

What is the ΔHf value for CO2?

The ΔHf value for CO2 is -394 kJ/mol, indicating that heat is released during its formation.

Why is the ΔHf value for elements defined as zero?

The ΔHf value for elements is defined as zero because they are formed from themselves, meaning there is no change in enthalpy.

What does a negative ΔH value indicate?

A negative ΔH value indicates that the reaction is exothermic, meaning heat is released to the surroundings.

In the example provided, what is the ΔH for the reaction involving NH3, O2, NO, and H2O?

For the reaction 4 NH3 + 5 O2 → 4 NO + 6 H2O, the calculated ΔH is -912 kJ.

How is the enthalpy change calculated for combustion reactions?

To calculate the enthalpy change for combustion reactions, the ΔHf values of the products and reactants are used in the same manner as other reactions, accounting for stoichiometric coefficients.