IB Chemistry Topic R1.2.3 Standard Enthalpy Changes of Combustion and Formation Revision Notes (HL)

IB Chemistry Topic R1.2.3 Standard Enthalpy Changes of Combustion and Formation Revision Notes (HL) | RevisionDojo

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Standard Enthalpy of Combustion ($ΔH_c^\circ$) and Formation ($ΔH_f^\circ$)

Both quantities are measured under standard conditions: a pressure of 100 kPa, with tabulated values usually quoted at 298 K.
The standard state of a substance is its most stable form under these conditions, for example O₂ as a gas, H₂O as a liquid, and carbon as graphite.

Standard Enthalpy of Combustion ($ΔH_c^\circ$)

Definition

Standard enthalpy of combustion

The standard enthalpy of combustion ($ΔH_c^\ominus$) is the energy change when one mole of a substance is completely burned in oxygen under standard conditions (298 K and 1 atm).

Complete combustion means every carbon atom is converted to CO₂ and every hydrogen atom to H₂O, with oxygen supplied in excess.
The products must be in their standard states, so CO₂ is a gas and H₂O is a liquid at 298 K.

Example

The combustion of methane (CH₄) is represented as:

$$\text{CH}_4(g) + 2\text{O}_2(g) \to \text{CO}_2(g) + 2\text{H}_2O(l) \quad \Delta H_c^\circ = -890 \, \text{kJ mol}^{-1}$$

This equation tells us that burning 1 mole of methane releases 890 kJ of energy.

Key Features of $ΔH_c^\circ$

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Standard Enthalpy of Combustion ($ΔH_c^\circ$) and Formation ($ΔH_f^\circ$)

Both quantities are measured under standard conditions: a pressure of 100 kPa, with tabulated values usually quoted at 298 K.
The standard state of a substance is its most stable form under these conditions, for example O₂ as a gas, H₂O as a liquid, and carbon as graphite.

Standard Enthalpy of Combustion ($ΔH_c^\circ$)

Definition

Standard enthalpy of combustion

The standard enthalpy of combustion ($ΔH_c^\ominus$) is the energy change when one mole of a substance is completely burned in oxygen under standard conditions (298 K and 1 atm).

Complete combustion means every carbon atom is converted to CO₂ and every hydrogen atom to H₂O, with oxygen supplied in excess.
The products must be in their standard states, so CO₂ is a gas and H₂O is a liquid at 298 K.

Example

The combustion of methane (CH₄) is represented as:

$$\text{CH}_4(g) + 2\text{O}_2(g) \to \text{CO}_2(g) + 2\text{H}_2O(l) \quad \Delta H_c^\circ = -890 \, \text{kJ mol}^{-1}$$

This equation tells us that burning 1 mole of methane releases 890 kJ of energy.

Key Features of $ΔH_c^\circ$

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Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics

IB Chemistry R1.2.3 Standard Enthalpy Changes of Combustion and Formation Notes

Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics

Standard Enthalpy of Combustion ($ΔH_c^\circ$) and Formation ($ΔH_f^\circ$)

Standard Enthalpy of Combustion ($ΔH_c^\circ$)

Key Features of $ΔH_c^\circ$

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Standard Enthalpy of Combustion ($ΔH_c^\circ$) and Formation ($ΔH_f^\circ$)

Standard Enthalpy of Combustion ($ΔH_c^\circ$)

Key Features of $ΔH_c^\circ$

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