PERSAMAAN TERMOKIMIA (KIMIA SMA KELAS 11)

Summary

This video script discusses thermochemical equations, which include enthalpy change data in chemical reactions. It explains the notation of phases and coefficients, the placement of enthalpy change values, and the significance of their signs indicating exothermic or endothermic reactions. Examples are provided, such as the combustion of methane and the synthesis of ammonia, to illustrate how to write thermochemical equations and the impact of scaling reactions on enthalpy values.

Takeaways

• 🔍 The script discusses thermochemical equations, which are chemical equations that include enthalpy change data.
• 📚 It explains that in thermochemical equations, the phase and coefficients of each substance involved must be included.
• 🔥 The enthalpy change (delta H) is written on the right side of the equation, slightly separated from the last product.
• ⬇️ For exothermic reactions, delta H is negative, and for endothermic reactions, it is positive.
• 🔄 The amount of substance involved in the reaction must equal the reaction's coefficients.
• 🌡 The magnitude of enthalpy depends on the amount of substance, its state (solid, liquid, or gas), and the condition of the system.
• 🔗 An example given is the reaction of two carbon atoms with hydrogen gas to form acetylene, with a positive enthalpy change of 227 kJ.
• 🔄 When thermochemical equations are multiplied by a factor, the enthalpy change must also be multiplied by that factor.
• 🔙 If the direction of a reaction is reversed, the sign of delta H changes; negative becomes positive and vice versa.
• 🧪 Practical examples are given, such as the reaction of baking soda with hydrochloric acid, which absorbs heat, and the formation and decomposition of water, with calculations for enthalpy changes.

Q & A

What is thermodynamic equilibrium?

Thermodynamic equilibrium refers to a state in a chemical reaction where the rates of the forward and reverse reactions are equal, and there is no net change in the concentrations of reactants and products.

How is enthalpy change related to the phase of substances?

Enthalpy change (ΔH) is related to the phase of substances in that the same chemical reaction can have different ΔH values depending on whether the substances are in solid, liquid, or gaseous states.

What is the significance of including phase and coefficients in a thermochemical equation?

Including phase and coefficients in a thermochemical equation is significant because it specifies the physical state of reactants and products and their stoichiometric ratios, which directly influence the enthalpy change of the reaction.

Why is it important to indicate the sign (positive or negative) of ΔH in a thermochemical equation?

The sign of ΔH indicates whether a reaction is exothermic (releases heat, ΔH is negative) or endothermic (absorbs heat, ΔH is positive), which is crucial for understanding the energy changes in a reaction.

How does the amount of substance (in moles) affect the enthalpy change of a reaction?

The amount of substance affects the enthalpy change because the total enthalpy change is proportional to the number of moles of reactants and products involved in the reaction.

What is the thermochemical equation for the combustion of methane?

The thermochemical equation for the combustion of methane is CH₄(g) + 2 O₂(g) → CO₂(g) + 2 H₂O(l) with ΔH representing the heat released during the reaction.

How does the enthalpy change value (ΔH) scale with the coefficients in a thermochemical equation?

The enthalpy change value (ΔH) scales directly with the coefficients in the thermochemical equation. If the coefficients are multiplied by a factor, ΔH must also be multiplied by that same factor.

What happens to the ΔH value if the direction of a reaction is reversed?

If the direction of a reaction is reversed, the sign of ΔH changes; if it was positive (endothermic), it becomes negative (exothermic), and vice versa.

Can you provide an example of a thermochemical equation for a reaction that absorbs heat?

An example of a thermochemical equation for an endothermic reaction is 2 C(s) + H₂(g) → C₂H₂(g) with ΔH = +227 kJ, indicating that heat is absorbed.

What is the thermochemical equation for the synthesis of ammonia, and what does the ΔH value represent?

The thermochemical equation for the synthesis of ammonia is N₂(g) + 3 H₂(g) → 2 NH₃(g) with ΔH = -91.8 kJ, representing the heat released during the formation of 2 moles of ammonia.