Textbook Question
Consider the following hypothetical reactions: A → B ΔH = +30 kJ B → C ΔH = +60 kJ (b) Construct an enthalpy diagram for substances A, B, and C, and show how Hess's law applies.
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Ch.5 - Thermochemistry
Chapter 5, Problem 65
The concentration of alcohol 1CH3CH2OH2 in blood, called the 'blood alcohol concentration' or BAC, is given in units of grams of alcohol per 100 mL of blood. The legal definition of intoxication, in many states of the United States, is that the BAC is 0.08 or higher. What is the concentration of alcohol, in terms of molarity, in blood if the BAC is 0.08?
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Identify the given BAC as 0.08 grams of alcohol per 100 mL of blood.
Convert the BAC from grams per 100 mL to grams per liter by multiplying by 10, since 1 L = 1000 mL.
Determine the molar mass of ethanol (CH3CH2OH) by adding the atomic masses of its constituent atoms: C, H, and O.
Convert the mass of ethanol in grams to moles using the formula: \( \text{moles} = \frac{\text{mass in grams}}{\text{molar mass}} \).
Calculate the molarity by dividing the number of moles of ethanol by the volume of the solution in liters.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Blood Alcohol Concentration (BAC)
Blood Alcohol Concentration (BAC) is a measure of the amount of alcohol present in a person's bloodstream, expressed in grams of alcohol per 100 mL of blood. A BAC of 0.08 means there are 0.08 grams of alcohol in every 100 mL of blood, which is a common legal threshold for intoxication in many jurisdictions.
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Rules for Naming Alcohols
Molarity
Molarity is a way to express the concentration of a solution, defined as the number of moles of solute per liter of solution. It is commonly used in chemistry to quantify the concentration of substances in a solution, allowing for easy calculations in chemical reactions and analyses.
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01:13Molarity
Conversion from grams to moles
To convert grams of a substance to moles, one must use the molar mass of the substance, which is the mass of one mole of that substance in grams. For ethanol (C2H5OH), the molar mass is approximately 46.07 g/mol. This conversion is essential for calculating molarity from a given mass concentration.
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Related Practice
Textbook Question
Calculate the enthalpy change for the reaction P4O6(s) + 2 O2(g) → P4O10(s) given the following enthalpies of reaction: P4(s) + 3 O2(g) → P4O6(s) ΔH = -1640.1 kJ P4(s) + 5 O2(g) → P4O10(s) ΔH = -2940.1 kJ
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Textbook Question
From the enthalpies of reaction 2 C(s) + O2(g) → 2 CO(g) ΔH = -221.0 kJ 2 C(s) + O2(g) + 4 H2(g) → 2 CH3OH(g) ΔH = -402.4 kJ Calculate ΔH for the reaction CO(g) + 2 H2(g) → CH3OH(g)
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Textbook Question
Given the data N2(g) + O2(g) → 2 NO(g) ΔH = +180.7 kJ 2 NO(g) + O2(g) → 2 NO2(g) ΔH = -113.1 kJ 2 N2O(g) → 2 N2(g) + O2(g) ΔH = -163.2 kJ use Hess's law to calculate ΔH for the reaction N2O(g) + NO2(g) → 3 NO(g)
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Textbook Question
We can use Hess's law to calculate enthalpy changes that cannot be measured. One such reaction is the conversion of methane to ethane: 2 CH4(g) → C2H6(g) + H2(g) Calculate the ΔH° for this reaction using the following thermochemical data: CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l) ΔH° = -890.3 kJ 2 H2(g) + O2(g) → 2 H2O(l) H° = -571.6 kJ 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(l) ΔH° = -3120.8 kJ
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Textbook Question
(c) What is meant by the term standard enthalpy of formation?
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