AP Chem Unit 6 Review | Thermochemistry in 10 Minutes - The First Law of Thermodynamics

What are the two types of thermochemical processes?

Exothermic and endothermic processes.

What happens to the surroundings during an endothermic process?

The surroundings get colder.

What occurs in an exothermic process?

Molecules lose energy to the surroundings.

How does heat transfer occur between warmer and cooler materials?

Heat is transferred from the warmer object to the cooler object until both temperatures equalize.

What does Q represent in thermochemistry?

The amount of heat transferred in joules.

What does ΔT represent in Q = mCΔT?

The change in temperature.

What condition must be met for heat transfer between two systems?

The heat gained by one system equals the heat lost by another.

During which phase changes does the temperature remain constant?

Melting and boiling.

What are exothermic processes during phase changes?

Condensation and freezing.

What does ΔH represent in a chemical reaction?

The heat change during a chemical reaction.

How can change in enthalpy be calculated using bond enthalpies?

Total energy of bonds broken minus total energy of bonds formed.

What is the formula for calculating heat transfer between two objects?

Q = mCΔT.

What happens when ionic compounds dissolve in water regarding energy?

They may break a high-energy bond, leading to a net endothermic process.

What does it mean for a reaction's enthalpy change to equal the sum of enthalpies of formation?

The change in enthalpy for a reaction is equal to the sum of the enthalpies of formation of the products minus that of the reactants.

What does a high bond enthalpy indicate?

It requires a lot of energy to break.

Where is the enthalpy of formation for an element in its most natural state found?

It is 0 kJ per mole.

What characteristic of the heating curve indicates an endothermic process?

Absorption of energy with constant temperature.

What is released when sodium reacts with chlorine gas?

Heat (822 kJ for the reaction of two moles of sodium).

What is the significance of Hess's law in thermochemistry?

It states that the total enthalpy change of a reaction is the sum of the enthalpy changes of individual steps.

What is thermal equilibrium?

A state when two objects reach the same temperature.

How can grams be converted to moles in specific heat calculations?

By using the molar mass of the substance.

What is specific heat capacity?

A measure of how well a material resists temperature change.

How can ΔH be calculated using reaction stoichiometry?

By converting grams of product to moles and applying the mole ratio for heat.

What is a transition state in a reaction energy diagram?

A temporary state during the transition from reactants to products at peak energy.

What is the effect on enthalpy during the breaking and forming of bonds in a reaction?

The reaction's enthalpy change depends on the energy of bonds broken and formed.

How is enthalpy change calculated using bond energies?

ΔH = Total bonds broken - Total bonds formed.

What happens to temperature during energy absorption in melting?

The temperature remains constant.

What is the heat of vaporization for water?

Positive 40.7 kJ per mole.

How do bond energies help in determining reaction energy?

By providing necessary values to calculate ΔH.

What does Q = mCΔT help calculate during heating processes?

The amount of heat transferred.

What is average kinetic energy another term for?

Temperature.

How is enthalpy change determined using standard enthalpies of formation?

By subtracting the sum of enthalpies of reactants from products.

What occurs during exothermic reactions?

Heat is released to the surroundings.

What needs to be done to apply Hess's law in reaction stoichiometry?

You may need to flip or multiply reactions.

What does a negative ΔH indicate?

The reaction is exothermic.

How do temperature changes relate to specific heat capacity?

Higher specific heat capacity means smaller temperature changes for the same heat added.

What effects do heating and cooling have on systems?

Systems absorb heat during endothermic reactions and release heat during exothermic reactions.

What features indicate an endothermic reaction when measuring temperature?

A net gain of potential energy and the cooling of surroundings.

How is a chemical reaction's enthalpy represented in equations?

ΔH, indicating heat change.

How does increasing temperature in a substance affect its molecular kinetic energy?

Higher temperature increases average kinetic energy of molecules.

What should be considered when calculating ΔH for reactions?

Bond enthalpy and molar relationships between reactants and products.

What causes the surroundings to feel warm during a chemical reaction?

Heat being released in an exothermic process.

How is the heat of condensation related to the heat of vaporization?

It is equal in magnitude but opposite in sign.

What happens when systems reach thermal equilibrium?

No net heat transfer occurs between them.

What is the term for the diagram illustrating energy changes during a reaction?

An energy diagram.

What role does a bond enthalpy table play in thermochemical calculations?

It provides values needed to calculate energy changes during reactions.