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Questions and Answers
What does the First Law of Thermodynamics primarily state?
What does the First Law of Thermodynamics primarily state?
- Heat energy always moves from cold to hot.
- Energy cannot be created or destroyed. (correct)
- Potential energy is the only form of energy considered.
- Chemical reactions release all energy as heat.
Which component contributes to heat transfer during a chemical reaction?
Which component contributes to heat transfer during a chemical reaction?
- The change in enthalpy during the reaction. (correct)
- The distance between reactant molecules.
- The color of the reactants.
- The pressure of the system.
For the combustion of octane, which process releases energy?
For the combustion of octane, which process releases energy?
- Breaking the bonds of the reactants.
- Increasing the pressure in the reaction vessel.
- Cooling the products after formation.
- Forming the bonds of the products. (correct)
How much energy is required to heat a 125 g piece of zinc from 23 °C to 125 °C?
How much energy is required to heat a 125 g piece of zinc from 23 °C to 125 °C?
Which liquid among the following requires the most energy to reach its boiling point?
Which liquid among the following requires the most energy to reach its boiling point?
What specific heat results from mixing a 65.39 g aluminum pellet at 80.0 °C with 500 g of water?
What specific heat results from mixing a 65.39 g aluminum pellet at 80.0 °C with 500 g of water?
When thermal equilibrium is reached, what happens to the temperatures of the substances involved?
When thermal equilibrium is reached, what happens to the temperatures of the substances involved?
What is the specific heat of water, used in calculations for thermal processes?
What is the specific heat of water, used in calculations for thermal processes?
What is the specific heat of the solution used in the calorimetry experiments?
What is the specific heat of the solution used in the calorimetry experiments?
During the calorimetry experiments, which type of calorimeter is primarily used for measuring reactions at constant pressure?
During the calorimetry experiments, which type of calorimeter is primarily used for measuring reactions at constant pressure?
In the dissolution of 10.0 g of NaOH, what is the sign of ΔrH° indicating the reaction's nature?
In the dissolution of 10.0 g of NaOH, what is the sign of ΔrH° indicating the reaction's nature?
What is the initial temperature of the ammonia solution before mixing with acetic acid?
What is the initial temperature of the ammonia solution before mixing with acetic acid?
What is the mass of water considered in the combustion of 3.50 g of FAME biofuel?
What is the mass of water considered in the combustion of 3.50 g of FAME biofuel?
What was the temperature change observed in the copper metal reaction with nickel(II) nitrate?
What was the temperature change observed in the copper metal reaction with nickel(II) nitrate?
How much energy is released when 10.0 g of NaNO3 dissolves in water with a ΔrH° of 20.5 kJ/mol?
How much energy is released when 10.0 g of NaNO3 dissolves in water with a ΔrH° of 20.5 kJ/mol?
What is the enthalpy of combustion for a sample if the temperature of the calorimeter reached 32.73 °C and the starting temperature was 23.00 °C?
What is the enthalpy of combustion for a sample if the temperature of the calorimeter reached 32.73 °C and the starting temperature was 23.00 °C?
What is the standard reaction enthalpy (ΔrHº) for the reaction 2 S (g) + 3 O2 (g) → 2 SO3 (g) using Hess's Law?
What is the standard reaction enthalpy (ΔrHº) for the reaction 2 S (g) + 3 O2 (g) → 2 SO3 (g) using Hess's Law?
Which step is necessary to determine the enthalpy for the reaction W (s) + C (s) → WC (s)?
Which step is necessary to determine the enthalpy for the reaction W (s) + C (s) → WC (s)?
How does Hess's Law contribute to calculating the overall reaction enthalpy?
How does Hess's Law contribute to calculating the overall reaction enthalpy?
Using the provided enthalpies of formation, what is the standard reaction enthalpy for the reaction CaO (g) + H2O (l) → Ca(OH)2 (s)?
Using the provided enthalpies of formation, what is the standard reaction enthalpy for the reaction CaO (g) + H2O (l) → Ca(OH)2 (s)?
In calculating the reaction enthalpy for combustion of naphthalene (C10H8), what is the enthalpy of formation for CO2?
In calculating the reaction enthalpy for combustion of naphthalene (C10H8), what is the enthalpy of formation for CO2?
What role do standard enthalpies of formation play in determining overall reaction enthalpy?
What role do standard enthalpies of formation play in determining overall reaction enthalpy?
When using Hess's Law, what is the result if a reaction is reversed?
When using Hess's Law, what is the result if a reaction is reversed?
How do variations in the enthalpies of formation affect the calculated enthalpy of a reaction?
How do variations in the enthalpies of formation affect the calculated enthalpy of a reaction?
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Study Notes
Thermochemistry
- The first law of thermodynamics, energy cannot be created or destroyed
- Energy is the ability to do work or transfer heat
- Energy is always conserved
- Isolated system does not exchange energy with the surroundings
Heat
- The amount of heat transferred is directly proportional to the change in temperature and the mass of the substance
- The amount of heat transferred is related to the specific heat of the substance
- Specific heat is the amount of heat required to raise the temperature of 1 gram of a substance by 1 degree Celsius
- For a given temperature change, a substance with a lower specific heat requires less heat to undergo the same change
Enthalpy
- Enthalpy is the heat content of a system at constant pressure
- Enthalpy change is the change in heat content of a system during a chemical reaction
- The sign of the enthalpy change indicates whether heat is released or absorbed
- Negative enthalpy change indicates heat is released from the system (exothermic)
- Positive enthalpy change indicates heat is absorbed by the system (endothermic)
Calorimetry
- Calorimetry is the study of heat transfer
- Calorimeters are used to measure the heat transferred during a chemical reaction
- There are two main types of calorimeters: constant pressure calorimeters and constant volume calorimeters
- Constant pressure calorimeter: a device that measures the heat transferred at constant pressure
- Constant volume calorimeter: a device that measures the heat transferred at constant volume
Hess's Law
- Hess's Law states that the enthalpy change of a reaction is independent of the pathway
- The enthalpy change of a reaction is equal to the sum of the enthalpy changes of the individual steps in the reaction
- Hess's Law is used to calculate the enthalpy change of a reaction that cannot be measured directly
Standard Enthalpy of Formation
- The standard enthalpy of formation (∆fHº) of a compound is the enthalpy change when 1 mole of the compound is formed from its elements in their standard states
- The standard enthalpy of formation of an element in its standard state is zero
- The standard enthalpy of formation can be used to calculate the enthalpy change of a reaction
Bond Energies
- Bond energy is the energy required to break a bond between two specific atoms
- Bond energies can be used to estimate the enthalpy change of a reaction
- Bond energy is a measure of the strength of a bond
State Functions
- A state function is a property that depends only on the initial and final states of a system, not on the pathway
- Enthalpy is a state function
- Internal pressure is a state function
- Entropy is a state function
- Volume is a state function
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