5. Reaction Enthalpy. balan and calculate AH for the following chemical equations. AHe (kJ/mol): HCN= 130. Ca3(PO4)2=-4120.8, H3PO4-1288, SiCl=-640.1, SiO₂= -910.9, Mg0=-601.6, HCl-167.1 d) MgO(s)+ H₂ H₂O(g) Mg(OH)2(s)
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
![### Reaction Enthalpy
**Objective:** Balance and calculate ΔH°_rxn_ for the following chemical equations.
### Standard Enthalpy of Formation (ΔH°_f_) Values (in kJ/mol):
- **HCN**: 130.5
- **Ca₃(PO₄)₂**: -4120.8
- **H₃PO₄**: -1288
- **SiCl₄**: -640.1
- **SiO₂**: -910.9
- **MgO**: -601.6
- **HCl**: -167.16
### Reaction:
\[ \text{d)} \quad \text{MgO(s) + H}_2\text{O(g) → Mg(OH)}_2\text{(s)} \]
### Instructions:
1. **Balance the equation**: Make sure all atoms are balanced on both sides of the reaction.
2. **Calculate ΔH°_rxn_**: Use the given standard enthalpy values to determine the reaction enthalpy.
### Calculating ΔH°_rxn_:
The standard reaction enthalpy is calculated using the formula:
\[ \Delta H^\circ_{\text{rxn}} = \sum \Delta H^\circ_f(\text{products}) - \sum \Delta H^\circ_f(\text{reactants}) \]
**Visual Representation:**
- **Reactants:** Magnesium oxide (MgO) in solid form and water (H₂O) in gaseous form.
- **Products:** Magnesium hydroxide (Mg(OH)₂) in solid form.
Understanding how to calculate reaction enthalpy is crucial for evaluating the energy changes involved in chemical reactions. This forms a fundamental part of thermodynamics in chemistry.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F5dbedc34-c1dd-4e16-ba9c-319b01d1eecb%2Ff3652351-14d9-40ef-9f47-e8af5cdfb4bd%2F3g2wcio_processed.jpeg&w=3840&q=75)
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