IB SL Chemistry - Reactivity 1.1

Where is chemical potential energy stored?

In the chemical bonds of reactants and products.

True or False: Temperature is a function of kinetic energy.

True

Describe exothermic reactions

Energy is released into the surroundings and bonds are formed. Note: the energy released from the formation of new bonds is greater than the energy required to break the existing bonds. (The system gets hotter and ΔH is negative.)

Describe endothermic reactions

Energy is absorbed from the surroundings and bonds are broken. Note: the energy released from the breaking of existing bonds is greater than the energy required to form new bonds. (The system gets colder and ΔH is positive.)

Describe the open system

Transfer of matter and energy is possible across the whole system.

Describe the closed system

No transfer of matter, but transfer of energy is possible across the whole system.Desccribe

Describe the isolated system

Matter and energy can neither enter nor exit.

What is a state function and give an example

When a change of value is independent of the pathway. Example: Temperature.

What is heat, q?

Heat is transformed (thermal or kinetic) energy from a warmer body to a cooler body (temperature gradient) in a system.

What is conduction?

In conduction, heat transfer occurs between objects by direct contact due to a temperature difference.

What is convection?

In convection, the heat transfer takes within the fluid due to a temperature difference.

What is radiation?

In radiation, heat transfer occurs through electromagnetic waves without involving particles.

What is the relationship between heat, work, kinetic energy and temperature?

Heat has the ability to do work. When heat is transferred to an object, the result is an increase in the average kinetic energy of its particles. Possibly causing an increase in temperature, or even a phase change.

What is entropy, S?

The measure of a system's thermal energy per unit temperature that is unavailable for doing useful work.

What is enthalpy, H?

Enthalpy is a measure of the heat content of a system at constant pressure.

What is the relationship between enthalpy change (ΔH) and heat (q)?

When a process occurs at constant pressure, the heat absorbed or released (q) by the system (from reactants to products) is directly equal to the change in enthalpy (ΔH, which is measured in kJ). 

What is a calorimeter?

A calorimeter is any apparatus used to measure the amount of heart being exchanged between the system and the surroundings.

What is bond dissociation energy?

The amount of energy needed to break a specific chemical bond in a molecule.

Energy profiles

A visual representation of the enthalpy change during a reaction.

Activation energy, E_a

The minimum energy required for the reaction to take place (from the energy level of reactants to the peak of the energy profile).

Describe the energy levels and stability of both reactants and products in exothermic reactions.

Reactants- higher energy level and less stable.

In exothermic reactions, energy is released from the system and into the surroundings.

Products- lower energy level and more stable.

Describe the energy levels and stability of both reactants and products in endothermic reactions.

Reactants- lower energy level and more stable.

In endothermic reactions, energy is absorbed from the surroundings and into the system.

Products- higher energy level and less stable.

Standard enthalpy change, ΔH°

Refers to the heat transferred at constant pressure under STP and standard states. Determined from the change in temperature of a pure substance. Units: kJ mol^-1

Specific heat capacity, c

The amount of heat needed to raise the temperature of 1kg of that substance by 1°C or 1K.

What is an intensive property and an example?

When the value does not change in magnitude with the size of the system being described. Example: specific heat capacity, c.W

What equation is used to calculate the amount of heat, Q, absorbed by a pure substance?

Q = mcΔT

What equation shows the relationship between heat, Q, and enthalpy change, ΔH?

ΔH = -(Q/n), where n is the number of moles of the limiting reactant.

True or False: Scientists usually make the assumption that the heat lost to the environment in calorimetry experiments is negligible.

Trrue- Calorimetry experiments typically give a smaller change in temperature than is predicted from theoretical values.