Methyl tert-butyl ether (MTBE), C5H12O, a gasoline additive used to boost octane ratings, has ΔH°f = -313.6 kJ/mol. Write a balanced equaiton for its combustion reaciton, and calcualte its standard heat of combustion in kilojoules
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Identify the chemical formula of Methyl tert-butyl ether (MTBE) and the products of its combustion. MTBE is C5H12O, and its combustion typically produces carbon dioxide (CO2) and water (H2O).
Write the unbalanced chemical equation for the combustion of MTBE: C5H12O + O2 -> CO2 + H2O.
Balance the chemical equation. Start by balancing the carbon atoms, then the hydrogen atoms, and finally the oxygen atoms. Adjust the coefficients accordingly to ensure the same number of each type of atom on both sides of the equation.
Use the balanced chemical equation to determine the stoichiometry of the reaction. This involves counting the moles of reactants and products involved in the reaction.
Calculate the standard heat of combustion (ΔH°comb) using the standard heat of formation (ΔH°f) values for all reactants and products. Apply Hess's Law: ΔH°comb = ΣΔH°f(products) - ΣΔH°f(reactants).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Combustion Reactions
Combustion reactions involve the reaction of a substance with oxygen, producing heat and light. In organic chemistry, these reactions typically yield carbon dioxide and water as products. For hydrocarbons and their derivatives, the general form of the reaction can be represented as: hydrocarbon + O2 → CO2 + H2O. Understanding this concept is essential for writing balanced equations for combustion.
The standard enthalpy of formation (ΔH°f) is the change in enthalpy when one mole of a compound is formed from its elements in their standard states. It is a crucial value for calculating the heat of reactions, including combustion. The ΔH°f values for reactants and products are used in Hess's law to determine the overall enthalpy change for a reaction, which is vital for calculating the standard heat of combustion.
Hess's Law states that the total enthalpy change for a reaction is the same, regardless of the number of steps taken to achieve the reaction. This principle allows chemists to calculate the enthalpy change of a reaction by using known ΔH°f values of the reactants and products. In the context of combustion, Hess's Law enables the determination of the standard heat of combustion by summing the enthalpy changes of formation for the products and subtracting those for the reactants.
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