3.2.1 - Enthalpy Changes Flashcards
What is enthalpy (H)?
Enthalpy is a measure of the total energy of a system, including internal energy and the energy required to displace its environment to make space for the system.
What is the enthalpy change (ΔH)?
The enthalpy change (ΔH) is the heat energy change that occurs in a reaction at constant pressure.
What is a positive enthalpy change?
A positive enthalpy change indicates that the reaction is endothermic, meaning heat is absorbed from the surroundings.
What is a negative enthalpy change?
A negative enthalpy change indicates that the reaction is exothermic, meaning heat is released to the surroundings.
What is the standard enthalpy of formation (ΔHf°)?
The standard enthalpy of formation is the enthalpy change when one mole of a substance is formed from its elements in their standard states under standard conditions (298 K, 1 atm pressure).
What is the standard enthalpy of combustion (ΔHc°)?
The standard enthalpy of combustion is the enthalpy change when one mole of a substance reacts completely with oxygen in its standard state under standard conditions.
What is the standard enthalpy of neutralization?
The standard enthalpy of neutralization is the enthalpy change when one mole of water is formed from the reaction between an acid and an alkali under standard conditions.
What is an exothermic reaction?
An exothermic reaction is a reaction in which energy (heat) is released to the surroundings, and the enthalpy change is negative (ΔH < 0).
What is an endothermic reaction?
An endothermic reaction is a reaction in which energy (heat) is absorbed from the surroundings, and the enthalpy change is positive (ΔH > 0).
How do you calculate enthalpy change (ΔH) using bond enthalpies?
The enthalpy change can be calculated using the formula:
ΔH = Σ(bond enthalpies of reactants) - Σ(bond enthalpies of products).
What is the Hess’s Law?
Hess’s Law states that the total enthalpy change of a reaction is the same, regardless of the pathway taken, as long as the initial and final conditions are the same.
What is the enthalpy of reaction?
The enthalpy of reaction is the enthalpy change that occurs when reactants are converted to products in a chemical reaction.
How can Hess’s Law be applied to calculate enthalpy changes?
Hess’s Law can be applied by using known enthalpy changes of other reactions to add or subtract them to find the enthalpy change of an unknown reaction.
What are standard conditions for measuring enthalpy changes?
Standard conditions are 298 K (25°C) temperature, 1 atm pressure, and concentrations of 1 mol/dm³ for solutions.
How do you determine the enthalpy change of combustion experimentally?
The enthalpy change of combustion can be determined using a calorimeter, where the heat released from a known mass of a substance burning is used to calculate the enthalpy change.
What is the bond dissociation enthalpy?
Bond dissociation enthalpy is the enthalpy change required to break one mole of a bond in a molecule in the gaseous state.
What is the relationship between bond enthalpies and enthalpy change?
Bond enthalpies are used to calculate the enthalpy change of a reaction by comparing the energy required to break bonds in reactants with the energy released when bonds are formed in products.
How is the enthalpy change of formation related to the enthalpy change of combustion?
The enthalpy change of formation is the enthalpy change when a compound is formed from its elements, while the enthalpy change of combustion is the enthalpy change when a substance is completely combusted in oxygen. These can be linked using Hess’s Law.
What is the formula to calculate enthalpy change using Hess’s Law?
The formula for Hess’s Law is:
ΔH (total) = ΣΔHf° (products) - ΣΔHf° (reactants).
What is the enthalpy change of solution?
The enthalpy change of solution is the enthalpy change when one mole of solute is dissolved in a solvent to form an infinitely dilute solution.
What is a calorimeter used for?
A calorimeter is an instrument used to measure the heat changes in physical or chemical processes, helping to calculate enthalpy changes experimentally.
What is the temperature change method to determine enthalpy change?
The temperature change method involves measuring the temperature change of the surroundings (such as water in a calorimeter) when a chemical reaction occurs. This allows the calculation of the heat energy transferred and the enthalpy change.
How does specific heat capacity relate to enthalpy change?
The specific heat capacity is the amount of heat required to raise the temperature of one gram of a substance by 1°C. It is used to calculate the heat energy transferred during a reaction in the temperature change method.
What factors can affect the enthalpy change of a reaction?
Factors that can affect enthalpy change include temperature, pressure, and concentration of reactants.
How can the enthalpy of formation be used in calculating enthalpy changes?
The enthalpy of formation can be used in conjunction with Hess’s Law to determine the enthalpy change of reactions by combining known formation enthalpies of products and reactants.
