Chemistry Notes

Flashcards about Hess's Law, Enthalpy Change, and Bond Energies in Chemistry.

What does a reaction pathway diagram show?

The energies of the reactants, transition state(s), and products of a reaction with time.

What is another name for reaction pathway diagrams?

Energy profile diagrams.

Define the transition state in a reaction.

A stage during the reaction at which chemical bonds are partially broken and formed.

Why is the transition state said to be very unstable?

Because it cannot be isolated and is higher in energy than the reactants and products

Define activation energy (Ea).

The minimum amount of energy needed for reactant molecules to have a successful collision and start the reaction.

In an exothermic reaction, how does the energy of the reactants compare to the products?

Reactants are higher in energy than the products.

How does the activation energy of exothermic reactions compare to endothermic reactions?

Exothermic reactions have a lower activation energy compared to endothermic reactions.

In an endothermic reaction, how does the energy of the reactants compare to the products?

The reactants are lower in energy than the products.

How does the activation energy of endothermic reactions compare to exothermic reactions?

Endothermic reactions have a higher activation energy compared to exothermic reactions.

What happens to bonds during reactions, causing enthalpy changes?

Bonds are being broken and formed.

Is bond breaking endothermic or exothermic?

Endothermic

Is bond forming endothermic or exothermic?

Exothermic

What is the relationship between energy required/released in bond breaking/forming and endothermic/exothermic reactions?

If more energy is required to break bonds than released when new bonds are formed, the reaction is endothermic. If more energy is released when new bonds are formed than required to break bonds, the reaction is exothermic.

Define Bond Dissociation Energy.

The amount of energy required to break one mole of a specific covalent bond in the gas phase

What is another term for bond dissociation energy?

Exact Bond Energy or Bond Enthalpy

What is average bond energy?

An average of a number of the same type of bond but in different environments

What is specific heat capacity (c)?

The energy needed to increase the temperature of 1 g of a substance by 1°C.

What is the formula for calculating energy transferred as heat?

q = m x c x ΔT, where q = heat transferred, m = mass of water, c = specific heat capacity, and ΔT = temperature change.