Ch 7 Thermochemistry Flashcards
Thermochemistry
What is thermochemistry?
The study of the heat involved in chemical reactions and changes of state.
True or False: Enthalpy is a measure of the heat content of a system.
True
What does the symbol ΔH represent?
The change in enthalpy.
Fill in the blank: Exothermic reactions release _____ to the surroundings.
heat
What is the formula for calculating heat (q) in thermochemistry?
q = m × c × ΔT
In an endothermic reaction, ΔH is _____?
positive
What is the standard enthalpy change of formation (ΔHf°)?
The change in enthalpy when one mole of a compound is formed from its elements in their standard states.
True or False: The enthalpy of reaction can be determined using Hess’s Law.
True
What is Hess’s Law?
The principle that the total enthalpy change for a reaction is the sum of the enthalpy changes for the individual steps.
What is a calorimeter used for?
To measure the heat absorbed or released during a chemical reaction.
Fill in the blank: The specific heat capacity of a substance is the amount of heat required to raise the temperature of _____ of that substance by _____ degree Celsius.
1 gram; 1
What does a negative ΔH indicate?
The reaction is exothermic.
What is the heat of fusion?
The amount of heat required to convert a unit mass of a solid into a liquid at its melting point.
What is the heat of vaporization?
The amount of heat required to convert a unit mass of a liquid into a vapor at its boiling point.
True or False: The heat of combustion is always negative.
True
What is the relationship between temperature and kinetic energy?
Temperature is a measure of the average kinetic energy of the particles in a substance.
What is the first law of thermodynamics?
Energy cannot be created or destroyed, only transformed from one form to another.
Fill in the blank: The term ‘system’ in thermochemistry refers to the part of the universe _____ to be studied.
chosen
What is a closed system?
A system that can exchange energy but not matter with its surroundings.
What is an open system?
A system that can exchange both energy and matter with its surroundings.
What is a thermochemical equation?
A balanced chemical equation that includes the enthalpy change.
True or False: The enthalpy change is independent of the pathway taken.
True
What are standard conditions in thermochemistry?
1 atm pressure and a specified temperature, usually 25°C (298 K).
What is the significance of the enthalpy of reaction?
It indicates whether a reaction is exothermic or endothermic.
What is meant by ‘enthalpy of solution’?
The change in enthalpy when a solute dissolves in a solvent.
Fill in the blank: The term ‘enthalpy change’ is often represented as _____ in chemical equations.
ΔH
What is the formula for calculating ΔH using bond energies?
ΔH = Σ(bond energies of reactants) - Σ(bond energies of products)
True or False: A higher specific heat capacity means a substance can absorb more heat without a significant temperature change.
True
What is the heat capacity of a substance?
The amount of heat required to raise the temperature of a given quantity of the substance by one degree Celsius.
What does the term ‘enthalpy of formation’ refer to?
The enthalpy change when one mole of a compound is formed from its elements in their standard states.
What is the difference between heat and temperature?
Heat is the energy transferred due to temperature difference, while temperature is a measure of the average kinetic energy of particles.
Fill in the blank: A substance with a high heat of vaporization requires _____ energy to change from liquid to gas.
more
What is the significance of the enthalpy of combustion?
It measures the energy released when a substance is burned in oxygen.
What does it mean when a reaction has a ΔH of 0?
The reaction is at equilibrium and there is no net change in enthalpy.
True or False: The enthalpy of a pure element in its standard state is defined as zero.
True
What is the relationship between enthalpy and temperature?
Enthalpy increases with an increase in temperature for a given amount of substance.
Fill in the blank: The law of conservation of energy states that energy cannot be _____ or _____; it can only be transformed.
created; destroyed
What is the equation for calculating work done on or by a gas?
W = -PΔV
What is the effect of pressure on enthalpy?
At constant pressure, the change in enthalpy equals the heat absorbed or released.
What does the term ‘spontaneous process’ refer to?
A process that occurs without external intervention.
What is Gibbs free energy?
A thermodynamic quantity that combines enthalpy and entropy to determine the spontaneity of a process.
True or False: A negative Gibbs free energy indicates a spontaneous reaction.
True
What is the formula for Gibbs free energy?
ΔG = ΔH - TΔS
Fill in the blank: The _____ of a reaction is a measure of the disorder of the system.
entropy
What does a positive ΔS indicate?
An increase in disorder or randomness in a system.
What is the significance of temperature in thermochemical reactions?
Temperature affects the rate of reactions and the direction of spontaneous processes.
What is the difference between specific heat and molar heat capacity?
Specific heat is per unit mass, while molar heat capacity is per mole of substance.
What is thermochemistry?
The study of energy changes during physical or chemical changes in matter
What do all thermodynamics depend on?
The law of conservation of energy
The law of conservation of energy states…
Energy cannot be created nor destroyed
Potential Energy (PE)
- Energy due to the position or composition of an object
- Stored Energy
Kinetic Energy (KE)
- Energy of motion
- Depends on mass of object and its velocity
Calculation of thermal energy
Thermal Energy=PE + KE
Changes that occur in matter may be classified into….
Physical, chemical or nuclear changes
Physical Change
- Change in form or state of a substance
- No chemical bonds are broken
- Least energy
Chemical Change
- Change in chemical bonds between atoms resulting in new substances
Nuclear Change
- Change in the protons or neutrons in an atom resulting in a new atom
- Most energy
What is a System?
The substance undergoing a change
What are the surroundings?
- Describes the system’s environment
- Includes all matter that is not part of the system
What is thermal energy?
- Total amount of movement (kinetic energy) of the particles in a system and the stored energy within these particles (potential energy)
What does thermal energy depend on?
- How many particles are moving and their temperature
What is temperature?
- Measures the average speed of particles in a sample
- Measured in ℃ or K
What is heat?
- The amount of thermal energy transferred between substances
- Due to a temperature difference
- Measured in Joules (J)
Extensive Property
- Directly depends upon the amount of substance
Example of an extensive property
Heat
Intensive Property
- Not related to the amount of the substance
Example of an intensive property
Temperature
State Function
Property that depends only on its current state and not on how that state was reached
Exothermic - Thermal energy (q)
Released
Exothermic - Direction of the flow of heat
System —> Surroundings
Exothermic - Temperature Change
- Tf>Ti
- ΔT>0
- Postive
Exothermic - Sign of ΔH
- ΔH<0
- Negative
Exothermic - Energy Term
- Product
- A + B —> C + energy
Endothermic - Thermal Energy (q)
Absorbed
Endothermic - Direction of the flow of heat
Surroundings —> System
Endothermic - Temperature Change
- Tf<Ti
- ΔT<0
- Negative
Endothermic - Sign of ΔH
- ΔH>0
- Postive
Endothermic - Energy Term
- Reactant
- A + Energy —> B + C
Open System
- Both matter and energy can move between the system and the surroundings
Open System Example
Boiling pot of water
Closed System
Can exchange energy but not matter with its surroundings
Closed System Example
Covered pot of water
Isolated System
- Neither energy nor matter can move into or out of the system
- Will still be some energy loss
Isolated System Example
Insulated thermos
