Ordinary level chemistry lesson notes

Ordinary level chemistry lesson notes

Ordinary level chemistry lesson notes

Boyle’s law.
Boyle’s law states that the volume (v) of a given mass of gas is inversely proportional to its
pressure (p) provided temperature is remain the same.
𝑡ℎ𝑎𝑡 𝑖𝑠, 𝑣 𝛼 1
𝑃
⇒ 𝑣 =
𝐾 𝑃
𝑜𝑟 𝑝𝑣 = 𝑘
The relationship can also be expressed mathematically as
P1V1 = P2V2
Note that, if the pressure of the gas is increases its volume decreases, and vice versa.
Exercise: if 65cm³ of an ideal gas exert a pressure of 375mmHg at 10 OC, the pressure that the
same gas will exert if its volume increases to 75cm³ at the same temperature will be.
Charles’ law
Charles’ law states that the volume of a given mass of gas is directly proportional to its
temperature provided the pressure remains constant

Topic 2: ENERGETICS (THERMOCHEMISTRY)
Thermochemistry is the study of heat change in chemical reactions.
ENTHALPY (𝑯)
It is the energy content of a system. It is denoted by H.
ENTHALPY CHANGE (∆𝑯)
The enthalpy change (or energy change) in a chemical reaction, denoted by ∆𝐻 (delta H), is the
difference between the enthalpies of the products and the enthalpies of the reactants.
i.e. ∆𝐻 = 𝐻(products) – 𝐻(reactants)
UNIT OF HEAT CHANGE OR ENTHALPY CHANGE
Heat change or enthalpy change ∆𝐻 is expressed in kilojoules per mole ( 𝐾𝐽/𝑚𝑜𝑙 𝑜𝑟 𝐾𝐽𝑚𝑜𝑙-1 )
Remark: 1KJ = 1000J
EXOTHERMIC REACTIONS
An exothermic reaction is one which gives out heat to the surroundings.
The enthalpy change, ∆𝐻 for an exothermic reaction is negative because the products have lower
enthalpies than the reactants. Example of exothermic reactions is:
1) 𝑁2(𝑔) + 3𝐻2(𝑔) → 2𝑁𝐻3(𝑔) ∆𝐻 = -92𝐾𝐽𝑚