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Questions and Answers
According to Hess's Law, what is the relationship between the total reaction enthalpy and the enthalpy changes of individual steps?
According to Hess's Law, what is the relationship between the total reaction enthalpy and the enthalpy changes of individual steps?
A state function changes depending on the path taken to reach a state.
A state function changes depending on the path taken to reach a state.
False
How do you calculate the heat released when 4 grams of H2O2 decomposes?
How do you calculate the heat released when 4 grams of H2O2 decomposes?
Heat Released = (0.12)(-187.8) = -22.54 kJ
The standard state enthalpy for monoatomic elements is _____
The standard state enthalpy for monoatomic elements is _____
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Match the terms with their appropriate definitions:
Match the terms with their appropriate definitions:
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What happens in an endothermic reaction?
What happens in an endothermic reaction?
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In an exothermic reaction, the products have higher potential energy than the reactants.
In an exothermic reaction, the products have higher potential energy than the reactants.
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What does the symbol ΔH represent in thermodynamics?
What does the symbol ΔH represent in thermodynamics?
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The specific heat of water is __________ than most substances.
The specific heat of water is __________ than most substances.
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Which technique is used to determine the heat change of a reaction?
Which technique is used to determine the heat change of a reaction?
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Match the following terms with their descriptions:
Match the following terms with their descriptions:
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Energy is always released during the formation of a bond.
Energy is always released during the formation of a bond.
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Using bond energies, ΔH can be calculated by subtracting the bond energies of the __________ from that of the __________.
Using bond energies, ΔH can be calculated by subtracting the bond energies of the __________ from that of the __________.
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What is the correct formula for calculating heat transfer in calorimetry?
What is the correct formula for calculating heat transfer in calorimetry?
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The surroundings in a calorimetry experiment only include the substances involved in the chemical reaction.
The surroundings in a calorimetry experiment only include the substances involved in the chemical reaction.
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What happens to the value of q when the concentration of reactants is doubled in a neutralization reaction?
What happens to the value of q when the concentration of reactants is doubled in a neutralization reaction?
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In calorimetry, the change in temperature is represented as ΔT, where ΔT = _____ - _____
In calorimetry, the change in temperature is represented as ΔT, where ΔT = _____ - _____
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Which statement about the molar enthalpy of neutralization (∆Hneut) is correct?
Which statement about the molar enthalpy of neutralization (∆Hneut) is correct?
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If significant heat is lost to the air during a calorimetry experiment, the calculated value of ∆Hneut will be higher than the actual value.
If significant heat is lost to the air during a calorimetry experiment, the calculated value of ∆Hneut will be higher than the actual value.
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How do you calculate the number of moles of water formed from a neutralization reaction between 1M HCl and 1M NaOH?
How do you calculate the number of moles of water formed from a neutralization reaction between 1M HCl and 1M NaOH?
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Study Notes
AP Chemistry Unit 5: Thermodynamics
- Test Format: 4-6 free response questions, 30-35 multiple choice questions
- Material Covered: Thermodynamics (80%), Stoichiometry, bonding, atomic, and reactions (20%)
- Study Resources: Practice free response questions, notes, homework, quizzes, reference sheets, and chemical reactions/atomic/bonding review assignments.
Heat vs. Temperature
- Heat: Transfer of thermal energy between systems measured in Joules (J) or Calories (cal).
- Temperature: Measures the average kinetic energy (KE) of particles within a substance, expressed in Fahrenheit, Celsius, or Kelvin.
- Relationship: When average KE doubles, Kelvin temperature also doubles. Kelvin is directly proportional to average KE.
Boltzmann Distribution
- Probability: Describes the probability of a system being in a particular state.
- Kinetic Energy Distribution: Displays the distribution of kinetic energy (KE) for a set of molecules at a given temperature.
- Molecular Collisions: Some particles collide and are deflected with high speeds, others nearly stop; some molecules reach a minimum activation energy (Ea) before reacting with the correct orientation.
Activation Energy (Ea)
- Definition: Minimum energy needed for a reaction to occur. It's the energy needed for molecules to collide with the correct orientation and form a transition complex.
- Transition Complex: Represents the unstable state where bonds are breaking and forming during a reaction.
- Examples: For a reaction to happen, molecules need to reach a certain activation energy threshold. Matches remain unlit without a spark and sunlight can break down substances in brown bottles.
Heat Transfer
- Conduction: Heat transfer between two systems in contact until thermal equilibrium is reached.
Conservation of Energy
- First Law: Energy cannot be created or destroyed.
- Change in Systems: Energy changes during chemical reactions and phase changes.
Endothermic vs. Exothermic Systems
- Endothermic: Systems absorb heat from the surroundings, products have greater potential energy than reactants
- Exothermic: Systems release heat to the surroundings, products have lower potential energy than reactants
Enthalpy (ΔH)
- Definition: Total internal energy of a system (sum of potential and kinetic energy).
- Extensive Property: Depends on the amount of substance.
- Intensive Property: Does not depend on the amount of substance.
Bond Enthalpy
- Average amount of energy needed to break a chemical bond
Specific Heat
- Heat energy required to raise the temperature of 1 gram of substance by 1°C (or 1 K). It measures a substance's ability to absorb or retain heat.
Calorimetry
- Techniques used to measure heat changes
- Quantifies the total heat transfer (q) given mass (m), specific heat (C), and change in temperature (ΔT)
Coffee Cup Calorimetry
- Measures heat transfer/exchange in aqueous reactions within a closed system
System vs Surroundings
- System: Specifies the specific process taking place
- Surroundings: Specifies area outside of the process
Gibbs Free Energy (ΔG)
- Equation: ΔG° = ΔH° - TΔS°
- Free Energy: Energy available to do work in a chemical reaction or process.
- ΔG < 0: Process can happen spontaneously.
- ΔG > 0: Process won't happen on its own, outside energy is needed.
Entropy (S)
- A measure of disorder in a system
- Measured in J/K mol
- Increased entropy leads to increase in microstates, a measure of possible arrangements of particles
- Entropy increases during heat absorption, chemical decomposition reactions, dissolution processes, phase transition processes(such as melting or vaporization), most chemical reactions
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Description
Test your understanding of thermodynamics in AP Chemistry Unit 5, which covers essential concepts such as heat, temperature, and Boltzmann distribution. This quiz includes various question formats to assess your grasp of key ideas and relationships in physical chemistry.
