Reaction Rates

What does the law of conservation of energy state?

Matter cannot be created nor can it be destroyed

What is the system of a reaction?

The substances directly involved in the reaction, including reactants and products

What is the surroundings in a reaction?

Everything outside of the system being studied

What is enthalpy?

The measurement of energy in a thermodynamic system

What is △H?

The change in enthalpy

• Negative for exothermic

• Positive for endothermic

What is temperature?

The measurement of average Kinetic Energy of a molecule or atom

Characteristics of endothermic reactions

Energy gained from surroundings

Feels cooler

Bonds of reactants > products

Characteristics of exothermic reactions

Energy lost to surroundings

Feels warmer

Bonds of reactants < products

What is the reaction rate?

A measure of the rate at which reactants are consumed and products are formed

What is needed for a successful reaction to occur? (collision theory)

Particles must collide;

at a suitable orientation;

with sufficient energy

What is activation energy? Why is it significant to reaction rate?

The minimum amount of energy that must be possessed by the reacting substances in order to form products

If activation energy is not enough, the reaction cannot occur naturally and requires input of additional energy

How does activation energy relate to the likelihood of a reaction occurring spontaneously?

If a reaction has a high activation energy, it is less likely to occur spontaneously. This indicates it is a slow reaction, requiring external energy input

If a reaction has a low activation energy, it is more likely to occur spontaneously. This indicates it is a fast reaction, not requiring external energy input

What is the transition state of a reaction?

The highest energy state for the reacting system:

• corresponds to the stage where bond breaking and formation is taking place

• is unstable, only existing momentarily as products are either being formed or broken

How are reaction rates affected by different factors?

Nature of reactants: strong/weak bonds

State of subdivision: size of reacting particles

Concentration: amount of particles in a given volume

Gas: in gaseous phase, more surface area

Temp: can 1) increase rate of reaction 2) increase number of sufficient particle collisions