Relate Enthalpy to Reactions - Chemistry
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What is the sign of $\Delta H_{fus}$ for melting a solid under typical conditions?
What is the sign of $\Delta H_{fus}$ for melting a solid under typical conditions?
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$\Delta H_{fus}>0$. Melting requires energy input, so positive.
$\Delta H_{fus}>0$. Melting requires energy input, so positive.
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What is the typical sign of $\Delta H_{comb}$ for a fuel undergoing complete combustion?
What is the typical sign of $\Delta H_{comb}$ for a fuel undergoing complete combustion?
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$\Delta H_{comb}<0$. Combustion reactions typically release energy.
$\Delta H_{comb}<0$. Combustion reactions typically release energy.
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Identify the sign of $\Delta H$ if products are at lower enthalpy than reactants on an energy diagram.
Identify the sign of $\Delta H$ if products are at lower enthalpy than reactants on an energy diagram.
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$\Delta H<0$. Lower energy products indicate exothermic reaction.
$\Delta H<0$. Lower energy products indicate exothermic reaction.
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Find the new $\Delta H$ if a reaction with $\Delta H=-80\ \mathrm{kJ}$ is multiplied by $3$.
Find the new $\Delta H$ if a reaction with $\Delta H=-80\ \mathrm{kJ}$ is multiplied by $3$.
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$\Delta H=-240\ \mathrm{kJ}$. Multiplying coefficients multiplies the enthalpy change.
$\Delta H=-240\ \mathrm{kJ}$. Multiplying coefficients multiplies the enthalpy change.
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What is the sign of $\Delta H_{vap}$ for boiling a liquid under typical conditions?
What is the sign of $\Delta H_{vap}$ for boiling a liquid under typical conditions?
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$\Delta H_{vap}>0$. Vaporization requires energy input, so positive.
$\Delta H_{vap}>0$. Vaporization requires energy input, so positive.
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What is the relationship between $\Delta H$ and heat flow if the system releases heat to the surroundings?
What is the relationship between $\Delta H$ and heat flow if the system releases heat to the surroundings?
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Heat released means $\Delta H<0$. Releasing heat corresponds to negative enthalpy change.
Heat released means $\Delta H<0$. Releasing heat corresponds to negative enthalpy change.
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What is the unit most commonly used for molar enthalpy changes in chemistry, such as $\Delta H$?
What is the unit most commonly used for molar enthalpy changes in chemistry, such as $\Delta H$?
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$\mathrm{kJ,mol^{-1}}$. Standard unit for enthalpy per mole in chemical reactions.
$\mathrm{kJ,mol^{-1}}$. Standard unit for enthalpy per mole in chemical reactions.
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Which sign of $\Delta H$ indicates an endothermic reaction process?
Which sign of $\Delta H$ indicates an endothermic reaction process?
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$\Delta H>0$. Positive $\Delta H$ means heat is absorbed from surroundings.
$\Delta H>0$. Positive $\Delta H$ means heat is absorbed from surroundings.
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Identify the enthalpy change name for converting $1$ mol of a solid to a liquid at its melting point.
Identify the enthalpy change name for converting $1$ mol of a solid to a liquid at its melting point.
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Enthalpy of fusion, $\Delta H_{fus}$. Energy required to convert solid to liquid.
Enthalpy of fusion, $\Delta H_{fus}$. Energy required to convert solid to liquid.
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Identify the enthalpy change name for converting $1$ mol of a liquid to a gas at its boiling point.
Identify the enthalpy change name for converting $1$ mol of a liquid to a gas at its boiling point.
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Enthalpy of vaporization, $\Delta H_{vap}$. Energy required to convert liquid to gas.
Enthalpy of vaporization, $\Delta H_{vap}$. Energy required to convert liquid to gas.
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What is the sign of $\Delta H_{fus}$ for melting a solid under typical conditions?
What is the sign of $\Delta H_{fus}$ for melting a solid under typical conditions?
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$\Delta H_{fus}>0$. Melting requires energy input, so positive.
$\Delta H_{fus}>0$. Melting requires energy input, so positive.
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What is the sign of $\Delta H_{vap}$ for boiling a liquid under typical conditions?
What is the sign of $\Delta H_{vap}$ for boiling a liquid under typical conditions?
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$\Delta H_{vap}>0$. Vaporization requires energy input, so positive.
$\Delta H_{vap}>0$. Vaporization requires energy input, so positive.
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Identify the enthalpy change name for dissolving $1$ mol of a solute in a solvent to infinite dilution.
Identify the enthalpy change name for dissolving $1$ mol of a solute in a solvent to infinite dilution.
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Enthalpy of solution, $\Delta H_{soln}$. Energy change when dissolving solute completely.
Enthalpy of solution, $\Delta H_{soln}$. Energy change when dissolving solute completely.
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What is the enthalpy change name for breaking $1$ mol of a specific bond in the gas phase?
What is the enthalpy change name for breaking $1$ mol of a specific bond in the gas phase?
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Bond enthalpy (bond dissociation enthalpy). Energy required to break one mole of bonds.
Bond enthalpy (bond dissociation enthalpy). Energy required to break one mole of bonds.
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State the bond enthalpy estimate formula for reaction enthalpy using bonds broken and formed.
State the bond enthalpy estimate formula for reaction enthalpy using bonds broken and formed.
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$\Delta H\approx\sum D(\text{broken})-\sum D(\text{formed})$. Energy to break bonds minus energy released forming bonds.
$\Delta H\approx\sum D(\text{broken})-\sum D(\text{formed})$. Energy to break bonds minus energy released forming bonds.
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Which is more exothermic: a reaction with $\Delta H=-50\ \mathrm{kJ}$ or $\Delta H=-10\ \mathrm{kJ}$?
Which is more exothermic: a reaction with $\Delta H=-50\ \mathrm{kJ}$ or $\Delta H=-10\ \mathrm{kJ}$?
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$\Delta H=-50\ \mathrm{kJ}$. Larger negative value means more heat released.
$\Delta H=-50\ \mathrm{kJ}$. Larger negative value means more heat released.
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Calculate $\Delta H_{rxn}$ if $H_{reactants}=120\ \mathrm{kJ}$ and $H_{products}=80\ \mathrm{kJ}$.
Calculate $\Delta H_{rxn}$ if $H_{reactants}=120\ \mathrm{kJ}$ and $H_{products}=80\ \mathrm{kJ}$.
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$\Delta H_{rxn}=-40\ \mathrm{kJ}$. Using $\Delta H = H_{products} - H_{reactants} = 80 - 120$.
$\Delta H_{rxn}=-40\ \mathrm{kJ}$. Using $\Delta H = H_{products} - H_{reactants} = 80 - 120$.
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Calculate $\Delta H_{rxn}$ if $H_{reactants}=55\ \mathrm{kJ}$ and $H_{products}=90\ \mathrm{kJ}$.
Calculate $\Delta H_{rxn}$ if $H_{reactants}=55\ \mathrm{kJ}$ and $H_{products}=90\ \mathrm{kJ}$.
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$\Delta H_{rxn}=+35\ \mathrm{kJ}$. Using $\Delta H = H_{products} - H_{reactants} = 90 - 55$.
$\Delta H_{rxn}=+35\ \mathrm{kJ}$. Using $\Delta H = H_{products} - H_{reactants} = 90 - 55$.
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Find $\Delta H$ for the reverse reaction if the forward reaction has $\Delta H=+125\ \mathrm{kJ}$.
Find $\Delta H$ for the reverse reaction if the forward reaction has $\Delta H=+125\ \mathrm{kJ}$.
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$\Delta H=-125\ \mathrm{kJ}$. Reversing a reaction changes the sign of $\Delta H$.
$\Delta H=-125\ \mathrm{kJ}$. Reversing a reaction changes the sign of $\Delta H$.
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Find the new $\Delta H$ if a reaction with $\Delta H=-80\ \mathrm{kJ}$ is multiplied by $3$.
Find the new $\Delta H$ if a reaction with $\Delta H=-80\ \mathrm{kJ}$ is multiplied by $3$.
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$\Delta H=-240\ \mathrm{kJ}$. Multiplying coefficients multiplies the enthalpy change.
$\Delta H=-240\ \mathrm{kJ}$. Multiplying coefficients multiplies the enthalpy change.
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Find the new $\Delta H$ if a reaction with $\Delta H=+60\ \mathrm{kJ}$ is multiplied by $\frac{1}{2}$.
Find the new $\Delta H$ if a reaction with $\Delta H=+60\ \mathrm{kJ}$ is multiplied by $\frac{1}{2}$.
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$\Delta H=+30\ \mathrm{kJ}$. Dividing coefficients divides the enthalpy change proportionally.
$\Delta H=+30\ \mathrm{kJ}$. Dividing coefficients divides the enthalpy change proportionally.
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What is $\Delta H$ for a reaction that releases $250\ \mathrm{kJ}$ of heat at constant pressure?
What is $\Delta H$ for a reaction that releases $250\ \mathrm{kJ}$ of heat at constant pressure?
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$\Delta H=-250\ \mathrm{kJ}$. Heat released means negative enthalpy change.
$\Delta H=-250\ \mathrm{kJ}$. Heat released means negative enthalpy change.
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What is $\Delta H$ for a reaction that absorbs $18\ \mathrm{kJ}$ of heat at constant pressure?
What is $\Delta H$ for a reaction that absorbs $18\ \mathrm{kJ}$ of heat at constant pressure?
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$\Delta H=+18\ \mathrm{kJ}$. Heat absorbed means positive enthalpy change.
$\Delta H=+18\ \mathrm{kJ}$. Heat absorbed means positive enthalpy change.
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Using Hess's law, find $\Delta H$ for $A\to C$ if $A\to B$ is $+40\ \mathrm{kJ}$ and $B\to C$ is $-15\ \mathrm{kJ}$.
Using Hess's law, find $\Delta H$ for $A\to C$ if $A\to B$ is $+40\ \mathrm{kJ}$ and $B\to C$ is $-15\ \mathrm{kJ}$.
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$\Delta H_{A\to C}=+25\ \mathrm{kJ}$. Using Hess's law: $40 + (-15) = +25$.
$\Delta H_{A\to C}=+25\ \mathrm{kJ}$. Using Hess's law: $40 + (-15) = +25$.
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Using Hess's law, find $\Delta H$ for $A\to C$ if $A\to B$ is $-10\ \mathrm{kJ}$ and $B\to C$ is $-35\ \mathrm{kJ}$.
Using Hess's law, find $\Delta H$ for $A\to C$ if $A\to B$ is $-10\ \mathrm{kJ}$ and $B\to C$ is $-35\ \mathrm{kJ}$.
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$\Delta H_{A\to C}=-45\ \mathrm{kJ}$. Using Hess's law: $(-10) + (-35) = -45$.
$\Delta H_{A\to C}=-45\ \mathrm{kJ}$. Using Hess's law: $(-10) + (-35) = -45$.
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Calculate $\Delta H_{rxn}^\circ$ given $\sum n\Delta H_f^\circ(\text{prod})=-500\ \mathrm{kJ}$ and $\sum n\Delta H_f^\circ(\text{react})=-200\ \mathrm{kJ}$.
Calculate $\Delta H_{rxn}^\circ$ given $\sum n\Delta H_f^\circ(\text{prod})=-500\ \mathrm{kJ}$ and $\sum n\Delta H_f^\circ(\text{react})=-200\ \mathrm{kJ}$.
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$\Delta H_{rxn}^\circ=-300\ \mathrm{kJ}$. Products minus reactants: $-500 - (-200) = -300$.
$\Delta H_{rxn}^\circ=-300\ \mathrm{kJ}$. Products minus reactants: $-500 - (-200) = -300$.
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Which sign of $\Delta H$ indicates an exothermic reaction process?
Which sign of $\Delta H$ indicates an exothermic reaction process?
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$\Delta H<0$. Negative $\Delta H$ means heat is released to surroundings.
$\Delta H<0$. Negative $\Delta H$ means heat is released to surroundings.
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What is the definition of the enthalpy change of reaction, $\Delta H_{rxn}$, at constant pressure?
What is the definition of the enthalpy change of reaction, $\Delta H_{rxn}$, at constant pressure?
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$\Delta H_{rxn}=H_{products}-H_{reactants}$ at constant $P$. Enthalpy change equals final enthalpy minus initial enthalpy.
$\Delta H_{rxn}=H_{products}-H_{reactants}$ at constant $P$. Enthalpy change equals final enthalpy minus initial enthalpy.
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Calculate $\Delta H_{rxn}^\circ$ given $\sum n\Delta H_f^\circ(\text{prod})=-120\ \mathrm{kJ}$ and $\sum n\Delta H_f^\circ(\text{react})=-300\ \mathrm{kJ}$.
Calculate $\Delta H_{rxn}^\circ$ given $\sum n\Delta H_f^\circ(\text{prod})=-120\ \mathrm{kJ}$ and $\sum n\Delta H_f^\circ(\text{react})=-300\ \mathrm{kJ}$.
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$\Delta H_{rxn}^\circ=+180\ \mathrm{kJ}$. Products minus reactants: $-120 - (-300) = +180$.
$\Delta H_{rxn}^\circ=+180\ \mathrm{kJ}$. Products minus reactants: $-120 - (-300) = +180$.
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Identify the sign of $\Delta H$ if products are at lower enthalpy than reactants on an energy diagram.
Identify the sign of $\Delta H$ if products are at lower enthalpy than reactants on an energy diagram.
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$\Delta H<0$. Lower energy products indicate exothermic reaction.
$\Delta H<0$. Lower energy products indicate exothermic reaction.
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