Enthalpy of Formation - AP Chemistry
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What is the sign of enthalpy for an exothermic formation reaction?
What is the sign of enthalpy for an exothermic formation reaction?
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Negative. Exothermic reactions release heat (negative $\Delta H$).
Negative. Exothermic reactions release heat (negative $\Delta H$).
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Identify the enthalpy change for the formation of 1 mole of $HCl(g)$ from $H_2(g)$ and $Cl_2(g)$.
Identify the enthalpy change for the formation of 1 mole of $HCl(g)$ from $H_2(g)$ and $Cl_2(g)$.
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-92.3 kJ/mol. Standard reference value for HCl gas formation enthalpy.
-92.3 kJ/mol. Standard reference value for HCl gas formation enthalpy.
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Describe the enthalpy of formation for a compound with high stability.
Describe the enthalpy of formation for a compound with high stability.
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Typically more negative. Stable compounds release more energy upon formation.
Typically more negative. Stable compounds release more energy upon formation.
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Calculate the enthalpy change for $N_2(g) + 3H_2(g) \rightarrow 2NH_3(g)$ given $\text{ΔH}_f^\text{°}(NH_3(g)) = -45.9$ kJ/mol.
Calculate the enthalpy change for $N_2(g) + 3H_2(g) \rightarrow 2NH_3(g)$ given $\text{ΔH}_f^\text{°}(NH_3(g)) = -45.9$ kJ/mol.
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-91.8 kJ/mol. Formation of 2 moles: $2 × (-45.9) = -91.8$ kJ.
-91.8 kJ/mol. Formation of 2 moles: $2 × (-45.9) = -91.8$ kJ.
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What is the unit for enthalpy of formation?
What is the unit for enthalpy of formation?
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kJ/mol. Energy per mole of substance formed.
kJ/mol. Energy per mole of substance formed.
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What is the standard enthalpy of formation ($\text{ΔH}_f^\text{°}$) for an element in its standard state?
What is the standard enthalpy of formation ($\text{ΔH}_f^\text{°}$) for an element in its standard state?
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0 kJ/mol. Elements in their standard state are the reference point (zero).
0 kJ/mol. Elements in their standard state are the reference point (zero).
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What is the enthalpy of formation for sodium chloride, $NaCl(s)$?
What is the enthalpy of formation for sodium chloride, $NaCl(s)$?
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-411 kJ/mol. Standard reference value for NaCl formation enthalpy.
-411 kJ/mol. Standard reference value for NaCl formation enthalpy.
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Define enthalpy of formation.
Define enthalpy of formation.
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Heat change when 1 mole of a compound forms from elements in standard states. The fundamental definition of $\Delta H_f^°$.
Heat change when 1 mole of a compound forms from elements in standard states. The fundamental definition of $\Delta H_f^°$.
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What is the enthalpy change when forming 1 mole of water from its elements under standard conditions?
What is the enthalpy change when forming 1 mole of water from its elements under standard conditions?
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-285.8 kJ/mol. Standard enthalpy of formation for liquid water.
-285.8 kJ/mol. Standard enthalpy of formation for liquid water.
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What is the enthalpy of formation for carbon monoxide, $CO(g)$?
What is the enthalpy of formation for carbon monoxide, $CO(g)$?
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-110.5 kJ/mol. Standard reference value for CO formation enthalpy.
-110.5 kJ/mol. Standard reference value for CO formation enthalpy.
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Calculate the standard enthalpy change for $C(s) + O_2(g) \rightarrow CO_2(g)$ given $\text{ΔH}_f^\text{°}(CO_2(g)) = -393.5$ kJ/mol.
Calculate the standard enthalpy change for $C(s) + O_2(g) \rightarrow CO_2(g)$ given $\text{ΔH}_f^\text{°}(CO_2(g)) = -393.5$ kJ/mol.
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-393.5 kJ/mol. Formation reaction equals the formation enthalpy directly.
-393.5 kJ/mol. Formation reaction equals the formation enthalpy directly.
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How is enthalpy of formation used in Hess's Law?
How is enthalpy of formation used in Hess's Law?
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To calculate enthalpy changes of reactions using known formation enthalpies. Formation enthalpies enable indirect enthalpy calculations.
To calculate enthalpy changes of reactions using known formation enthalpies. Formation enthalpies enable indirect enthalpy calculations.
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Identify the enthalpy change for forming 1 mole of $CH_3OH(l)$ from its elements.
Identify the enthalpy change for forming 1 mole of $CH_3OH(l)$ from its elements.
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-238.7 kJ/mol. Standard reference value for methanol formation enthalpy.
-238.7 kJ/mol. Standard reference value for methanol formation enthalpy.
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What is the enthalpy of formation for hydrochloric acid in aqueous solution, $HCl(aq)$?
What is the enthalpy of formation for hydrochloric acid in aqueous solution, $HCl(aq)$?
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-167.2 kJ/mol. Aqueous HCl has different enthalpy than gas phase.
-167.2 kJ/mol. Aqueous HCl has different enthalpy than gas phase.
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Calculate the enthalpy change for $2H_2(g) + O_2(g) \rightarrow 2H_2O(l)$ given $\text{ΔH}_f^\text{°}(\text{H}_2O(l)) = -285.8$ kJ/mol.
Calculate the enthalpy change for $2H_2(g) + O_2(g) \rightarrow 2H_2O(l)$ given $\text{ΔH}_f^\text{°}(\text{H}_2O(l)) = -285.8$ kJ/mol.
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-571.6 kJ/mol. Formation of 2 moles: $2 × (-285.8) = -571.6$ kJ.
-571.6 kJ/mol. Formation of 2 moles: $2 × (-285.8) = -571.6$ kJ.
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What is the standard enthalpy of formation for oxygen gas, $O_2(g)$?
What is the standard enthalpy of formation for oxygen gas, $O_2(g)$?
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0 kJ/mol. Diatomic oxygen is an element in its standard state.
0 kJ/mol. Diatomic oxygen is an element in its standard state.
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Identify the standard conditions for measuring enthalpy of formation.
Identify the standard conditions for measuring enthalpy of formation.
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1 atm pressure, 25°C (298 K). Standard temperature and pressure conditions for thermodynamics.
1 atm pressure, 25°C (298 K). Standard temperature and pressure conditions for thermodynamics.
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Identify the enthalpy change for forming 1 mole of $C_2H_5OH(l)$ from its elements.
Identify the enthalpy change for forming 1 mole of $C_2H_5OH(l)$ from its elements.
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-277.38 kJ/mol. Standard reference value for ethanol formation enthalpy.
-277.38 kJ/mol. Standard reference value for ethanol formation enthalpy.
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Which process typically has a positive enthalpy of formation: formation of bonds or breaking bonds?
Which process typically has a positive enthalpy of formation: formation of bonds or breaking bonds?
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Breaking bonds. Bond breaking requires energy input (endothermic).
Breaking bonds. Bond breaking requires energy input (endothermic).
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What is the enthalpy of formation for methane, $CH_4(g)$?
What is the enthalpy of formation for methane, $CH_4(g)$?
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-74.8 kJ/mol. Standard reference value for methane formation enthalpy.
-74.8 kJ/mol. Standard reference value for methane formation enthalpy.
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What is the standard enthalpy of formation for glucose, $C_6H_{12}O_6(s)$?
What is the standard enthalpy of formation for glucose, $C_6H_{12}O_6(s)$?
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-1273 kJ/mol. Standard reference value for glucose formation enthalpy.
-1273 kJ/mol. Standard reference value for glucose formation enthalpy.
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What is the enthalpy of formation for benzene, $C_6H_6(l)$?
What is the enthalpy of formation for benzene, $C_6H_6(l)$?
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49.0 kJ/mol. Standard reference value for benzene formation enthalpy.
49.0 kJ/mol. Standard reference value for benzene formation enthalpy.
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What is the enthalpy of formation for sulfur dioxide, $SO_2(g)$?
What is the enthalpy of formation for sulfur dioxide, $SO_2(g)$?
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-296.8 kJ/mol. Standard reference value for SO₂ formation enthalpy.
-296.8 kJ/mol. Standard reference value for SO₂ formation enthalpy.
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What is the enthalpy of formation for hydrogen peroxide, $H_2O_2(l)$?
What is the enthalpy of formation for hydrogen peroxide, $H_2O_2(l)$?
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-187.8 kJ/mol. Standard reference value for H₂O₂ formation enthalpy.
-187.8 kJ/mol. Standard reference value for H₂O₂ formation enthalpy.
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What is the enthalpy of formation for hydrogen gas, $H_2(g)$?
What is the enthalpy of formation for hydrogen gas, $H_2(g)$?
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0 kJ/mol. Diatomic hydrogen is an element in its standard state.
0 kJ/mol. Diatomic hydrogen is an element in its standard state.
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Which substance has an enthalpy of formation of 0: $N_2(g)$, $N_2O(g)$, or $NH_3(g)$?
Which substance has an enthalpy of formation of 0: $N_2(g)$, $N_2O(g)$, or $NH_3(g)$?
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$N_2(g)$. Nitrogen gas is an element in its standard state.
$N_2(g)$. Nitrogen gas is an element in its standard state.
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What is the enthalpy of formation for nitric oxide, $NO(g)$?
What is the enthalpy of formation for nitric oxide, $NO(g)$?
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90.3 kJ/mol. Standard reference value for NO formation enthalpy.
90.3 kJ/mol. Standard reference value for NO formation enthalpy.
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What is the sign of enthalpy for an exothermic formation reaction?
What is the sign of enthalpy for an exothermic formation reaction?
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Negative. Exothermic reactions release heat (negative $\Delta H$).
Negative. Exothermic reactions release heat (negative $\Delta H$).
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What is the enthalpy of formation for nitrogen dioxide, $NO_2(g)$?
What is the enthalpy of formation for nitrogen dioxide, $NO_2(g)$?
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33.2 kJ/mol. Standard reference value for NO₂ formation enthalpy.
33.2 kJ/mol. Standard reference value for NO₂ formation enthalpy.
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State the formula for calculating the enthalpy change of a reaction using formation enthalpies.
State the formula for calculating the enthalpy change of a reaction using formation enthalpies.
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$\text{ΔH}_\text{reaction} = \text{ΣΔH}_f^\text{°}(\text{products}) - \text{ΣΔH}_f^\text{°}(\text{reactants})$. Sum product enthalpies, subtract reactant enthalpies.
$\text{ΔH}_\text{reaction} = \text{ΣΔH}_f^\text{°}(\text{products}) - \text{ΣΔH}_f^\text{°}(\text{reactants})$. Sum product enthalpies, subtract reactant enthalpies.
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