AP Chemistry Flashcards: Introduction To Enthalpy Of Reaction

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This deck focuses on Introduction To Enthalpy Of Reaction, giving you a quick way to review the definitions, rules, and examples that matter most for AP Chemistry.

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Flashcard 1: What is the enthalpy change for the conversion of diamond to graphite?

Answer: $\Delta H = -1.9$ kJ/mol. Slightly exothermic carbon allotrope transformation.

Flashcard 2: Define the term 'standard state' in the context of enthalpy.

Answer: It is the physical state of a substance at 1 atm and 25°C. Reference conditions for comparing thermodynamic properties.

Flashcard 3: Identify the enthalpy change for the evaporation of water.

Answer: $\Delta H_{vap} = 40.7$ kJ/mol. Energy required for liquid-to-gas phase transition.

Flashcard 4: What does a positive $\Delta H$ indicate about a reaction?

Answer: A positive $\Delta H$ indicates an endothermic reaction. Heat is absorbed from the surroundings during the reaction.

Flashcard 5: What is the significance of a large negative $\Delta H$ value?

Answer: It indicates a strongly exothermic reaction. Large energy release indicates highly favorable reaction.

Flashcard 6: Which type of reaction absorbs heat from the surroundings?

Answer: Endothermic reactions absorb heat. Positive $\Delta H$ indicates heat absorption from surroundings.

Flashcard 7: State Hess's Law.

Answer: The total enthalpy change is the same, regardless of the pathway taken. Fundamental principle allowing indirect enthalpy calculations.

Flashcard 8: What is the enthalpy of fusion?

Answer: It is the enthalpy change when one mole of solid turns into liquid. Melting process requiring energy input for phase change.

Flashcard 9: What is the enthalpy change when 1 mol of water forms from hydrogen and oxygen?

Answer: $\Delta H_f^\circ = -285.8$ kJ/mol. Standard formation enthalpy for liquid water from elements.

Flashcard 10: What is the relationship between $\Delta H$ and $q$ at constant pressure?

Answer: $\Delta H = q$ at constant pressure. Direct equivalence when pressure remains constant throughout.

Flashcard 11: What does a negative $\Delta H$ signify about a reaction?

Answer: A negative $\Delta H$ indicates an exothermic reaction. Heat is released to the surroundings during the reaction.

Flashcard 12: What is the definition of enthalpy (H)?

Answer: Enthalpy (H) is the heat content of a system at constant pressure. Represents total internal energy plus pressure-volume work.

Flashcard 13: What is the enthalpy of fusion?

Answer: It is the enthalpy change when one mole of solid turns into liquid. Melting process requiring energy input for phase change.

Flashcard 14: What is the standard enthalpy change of formation for an element in its standard state?

Answer: It is zero. Elements in standard states are reference points.

Flashcard 15: What does the symbol $\Delta H_{rxn}$ represent?

Answer: It represents the enthalpy change for a chemical reaction. Standard notation for reaction enthalpy under specified conditions.

Flashcard 16: What is the enthalpy change for the conversion of diamond to graphite?

Answer: $\Delta H = -1.9$ kJ/mol. Slightly exothermic carbon allotrope transformation.

Flashcard 17: Define the term 'standard state' in the context of enthalpy.

Answer: It is the physical state of a substance at 1 atm and 25°C. Reference conditions for comparing thermodynamic properties.

Flashcard 18: State the enthalpy change for the formation of one mole of carbon dioxide from carbon and oxygen.

Answer: $\Delta H_f^\circ = -393.5$ kJ/mol. Standard formation enthalpy for carbon dioxide from elements.

Flashcard 19: What is meant by 'enthalpy of combustion'?

Answer: It is the enthalpy change when one mole of a substance burns completely in oxygen. Complete oxidation reaction with oxygen as the oxidizing agent.

Flashcard 20: Identify the process with $\Delta H_{sub} = \Delta H_{fus} + \Delta H_{vap}$.

Answer: Sublimation. Relationship connects fusion and vaporization enthalpies.

Flashcard 21: What is the standard enthalpy change of formation ($\Delta H_f^\circ$)?

Answer: It is the enthalpy change when one mole of a compound forms from its elements in their standard states. Standard reference point for calculating reaction enthalpies.

Flashcard 22: What is the enthalpy change for the conversion of diamond to graphite?

Answer: $\Delta H = -1.9$ kJ/mol. Slightly exothermic carbon allotrope transformation.

Flashcard 23: What is meant by 'enthalpy of combustion'?

Answer: It is the enthalpy change when one mole of a substance burns completely in oxygen. Complete oxidation reaction with oxygen as the oxidizing agent.

Flashcard 24: What is the standard enthalpy change of formation ($\Delta H_f^\circ$)?

Answer: It is the enthalpy change when one mole of a compound forms from its elements in their standard states. Standard reference point for calculating reaction enthalpies.

Flashcard 25: Calculate the $\Delta H$ for a reaction using Hess's Law given multiple reactions.

Answer: Add individual $\Delta H$ values to find total $\Delta H$. Sum intermediate steps to find overall enthalpy change.

Flashcard 26: What is meant by 'enthalpy of combustion'?

Answer: It is the enthalpy change when one mole of a substance burns completely in oxygen. Complete oxidation reaction with oxygen as the oxidizing agent.

Flashcard 27: What is the enthalpy change for the reaction of hydrogen with chlorine to form HCl?

Answer: $\Delta H = -184.6$ kJ/mol. Exothermic formation of hydrogen chloride from elements.

Flashcard 28: Identify the enthalpy change for the evaporation of water.

Answer: $\Delta H_{vap} = 40.7$ kJ/mol. Energy required for liquid-to-gas phase transition.

Flashcard 29: Identify the components in the enthalpy change equation $\Delta H = q_p$.

Answer: $q_p$ represents the heat absorbed or released at constant pressure. Heat transfer equals enthalpy change at constant pressure.

Flashcard 30: Define the term 'standard state' in the context of enthalpy.

Answer: It is the physical state of a substance at 1 atm and 25°C. Reference conditions for comparing thermodynamic properties.

Flashcard 31: Which type of reaction absorbs heat from the surroundings?

Answer: Endothermic reactions absorb heat. Positive $\Delta H$ indicates heat absorption from surroundings.

Flashcard 32: Calculate $\Delta H$ using calorimetry data for a reaction.

Answer: Use $q = mc\Delta T$ and $\Delta H = \frac{q}{n}$, where $n$ is moles. Combine heat capacity data with molar quantities.

Flashcard 33: What is the significance of enthalpy in chemical reactions?

Answer: Enthalpy helps predict the heat exchange and spontaneity of reactions. Determines energy requirements and reaction feasibility.

Flashcard 34: Identify the units typically used for enthalpy in chemistry.

Answer: The units are usually kilojoules per mole (kJ/mol). Energy per amount of substance in standard scientific notation.

Flashcard 35: Identify the components in the enthalpy change equation $\Delta H = q_p$.

Answer: $q_p$ represents the heat absorbed or released at constant pressure. Heat transfer equals enthalpy change at constant pressure.

Flashcard 36: What is the enthalpy change when one mole of ice melts to water at 0°C?

Answer: $\Delta H_{fus} = 6.01$ kJ/mol. Energy required for solid-to-liquid phase transition.

Flashcard 37: What is the enthalpy of neutralization?

Answer: It is the enthalpy change when an acid and a base react to form water. Acid-base reaction forming water as the primary product.

Flashcard 38: Identify the components in the enthalpy change equation $\Delta H = q_p$.

Answer: $q_p$ represents the heat absorbed or released at constant pressure. Heat transfer equals enthalpy change at constant pressure.

Flashcard 39: What is the enthalpy of neutralization?

Answer: It is the enthalpy change when an acid and a base react to form water. Acid-base reaction forming water as the primary product.

Flashcard 40: What is the enthalpy change when 1 mol of water forms from hydrogen and oxygen?

Answer: $\Delta H_f^\circ = -285.8$ kJ/mol. Standard formation enthalpy for liquid water from elements.

Flashcard 41: What is the definition of enthalpy (H)?

Answer: Enthalpy (H) is the heat content of a system at constant pressure. Represents total internal energy plus pressure-volume work.

Flashcard 42: What is the definition of enthalpy (H)?

Answer: Enthalpy (H) is the heat content of a system at constant pressure. Represents total internal energy plus pressure-volume work.

Flashcard 43: What is the enthalpy of vaporization?

Answer: It is the enthalpy change when one mole of liquid turns into gas. Evaporation process requiring energy input for phase change.

Flashcard 44: Calculate the enthalpy change for a reaction if $q = 250$ J and $n = 0.5$ mol.

Answer: $\Delta H = 500$ J/mol. Using $\Delta H = \frac{q}{n} = \frac{250}{0.5}$.

Flashcard 45: Calculate the enthalpy change for a reaction if $q = 250$ J and $n = 0.5$ mol.

Answer: $\Delta H = 500$ J/mol. Using $\Delta H = \frac{q}{n} = \frac{250}{0.5}$.

Flashcard 46: What is the significance of a large negative $\Delta H$ value?

Answer: It indicates a strongly exothermic reaction. Large energy release indicates highly favorable reaction.

Flashcard 47: What is the enthalpy change when one mole of ice melts to water at 0°C?

Answer: $\Delta H_{fus} = 6.01$ kJ/mol. Energy required for solid-to-liquid phase transition.

Flashcard 48: Calculate the $\Delta H$ for the decomposition of $2$ moles of $H_2O_2$ given $\Delta H = -196$ kJ/mol.

Answer: $\Delta H = -392$ kJ. Multiply per-mole enthalpy by number of moles reacting.

Flashcard 49: Which type of reaction absorbs heat from the surroundings?

Answer: Endothermic reactions absorb heat. Positive $\Delta H$ indicates heat absorption from surroundings.

Flashcard 50: What is the significance of a large negative $\Delta H$ value?

Answer: It indicates a strongly exothermic reaction. Large energy release indicates highly favorable reaction.

Flashcard 51: Which type of reaction releases heat to the surroundings?

Answer: Exothermic reactions release heat. Negative $\Delta H$ indicates heat release to surroundings.

Flashcard 52: What is the enthalpy change ($\Delta H$) when one mole of water vapor condenses?

Answer: $\Delta H = -40.7$ kJ/mol. Reverse of vaporization with opposite sign.

Flashcard 53: Identify the enthalpy change for the evaporation of water.

Answer: $\Delta H_{vap} = 40.7$ kJ/mol. Energy required for liquid-to-gas phase transition.

Flashcard 54: What is meant by 'enthalpy of sublimation'?

Answer: It is the enthalpy change when a solid changes directly to a gas. Direct solid-to-gas phase transition bypassing liquid phase.

Flashcard 55: Calculate $\Delta H$ using calorimetry data for a reaction.

Answer: Use $q = mc\Delta T$ and $\Delta H = \frac{q}{n}$, where $n$ is moles. Combine heat capacity data with molar quantities.

Flashcard 56: Find the enthalpy change for the reaction given $H_{products} = 100$ kJ and $H_{reactants} = 150$ kJ.

Answer: $\Delta H = -50$ kJ. Using $\Delta H = H_{products} - H_{reactants} = 100 - 150$.

Flashcard 57: What is the enthalpy of fusion?

Answer: It is the enthalpy change when one mole of solid turns into liquid. Melting process requiring energy input for phase change.

Flashcard 58: What is the relationship between $\Delta H$ and $q$ at constant pressure?

Answer: $\Delta H = q$ at constant pressure. Direct equivalence when pressure remains constant throughout.

Flashcard 59: State the formula for change in enthalpy ($\Delta H$).

Answer: $\Delta H = H_{products} - H_{reactants}$. Difference between final and initial enthalpy states.

Flashcard 60: Calculate $\Delta H$ using calorimetry data for a reaction.

Answer: Use $q = mc\Delta T$ and $\Delta H = \frac{q}{n}$, where $n$ is moles. Combine heat capacity data with molar quantities.

Flashcard 61: What are standard conditions for measuring enthalpy changes?

Answer: Standard conditions are 1 atm pressure and 25°C temperature. Standard reference conditions for thermodynamic measurements.

Flashcard 62: What is the enthalpy change when one mole of ice melts to water at 0°C?

Answer: $\Delta H_{fus} = 6.01$ kJ/mol. Energy required for solid-to-liquid phase transition.

Flashcard 63: What is the enthalpy change when 1 mol of water forms from hydrogen and oxygen?

Answer: $\Delta H_f^\circ = -285.8$ kJ/mol. Standard formation enthalpy for liquid water from elements.

Flashcard 64: Calculate the $\Delta H$ for a reaction using Hess's Law given multiple reactions.

Answer: Add individual $\Delta H$ values to find total $\Delta H$. Sum intermediate steps to find overall enthalpy change.

Flashcard 65: What does a negative $\Delta H$ signify about a reaction?

Answer: A negative $\Delta H$ indicates an exothermic reaction. Heat is released to the surroundings during the reaction.

Flashcard 66: Calculate the $\Delta H$ for a reaction using Hess's Law given multiple reactions.

Answer: Add individual $\Delta H$ values to find total $\Delta H$. Sum intermediate steps to find overall enthalpy change.

Flashcard 67: What does a negative $\Delta H$ signify about a reaction?

Answer: A negative $\Delta H$ indicates an exothermic reaction. Heat is released to the surroundings during the reaction.

Flashcard 68: What is the significance of a reaction's enthalpy change being zero?

Answer: It indicates no net heat change; the system is at equilibrium. No net energy transfer occurs during the process.

Flashcard 69: Calculate the enthalpy change for a reaction if $q = 250$ J and $n = 0.5$ mol.

Answer: $\Delta H = 500$ J/mol. Using $\Delta H = \frac{q}{n} = \frac{250}{0.5}$.

Flashcard 70: Which principle states that the total energy of an isolated system remains constant?

Answer: The First Law of Thermodynamics. Conservation of energy in closed systems.

Flashcard 71: What is the enthalpy of neutralization?

Answer: It is the enthalpy change when an acid and a base react to form water. Acid-base reaction forming water as the primary product.

Flashcard 72: What is the relationship between $\Delta H$ and $q$ at constant pressure?

Answer: $\Delta H = q$ at constant pressure. Direct equivalence when pressure remains constant throughout.