Which of the following reactions are exothermic?

 

$$\begin{gathered} 1) C + O2 → CO2 \\ 2) 2Mg + O2 → 2MgO \\ 3) CuSO4 + 5H2O → CuSO4.5H2O \\ 4) All the above \end{gathered}$$

There are two types of water hardness: temporary and permanent hardness. Temporary hardness is due to the presence of calcium hydrogen carbonate Ca(HCO3)2(aq) and magnesium hydrogen carbonate Mg(HCO3)2(aq).

A mixture is made from different substances that are not chemically joined.Compound:

•Two or more elements combine together chemically to form a new substance called compound.

•The different elements are chemically joined together.•Compounds are homogeneous, i.e. their properties are the same throughout

•The compound has properties different from the elements it contains.

•It can only be separated into its elements using chemical reactions. (not using physical methods)

•During the formation of a compound from its elements, a certain amount of energy in the form of heat, light, electricity is either absorbed or evolved

Lord Kelvin, working in Scotland, developed the Kelvin scale in 1848. His scale uses molecular energy to define the extremes of hot and cold. Absolute zero, or 0 K, corresponds to the point at which molecular energy is at a minimum. The Kelvin scale is preferred in scientific work, although the Celsius scale is also commonly used. Temperatures measured on the Kelvin scale are reported simply as K, not °K.

T (in °C) + 273.15 = T (in K)

T (in K) − 273.15 = T (in °C)

Argon gas is used in fluorescent and incandescent light bulbs to stop the oxygen in the light bulbs from corroding the hot tungsten filament.

The use of argon in light bulbs prevents the evaporation of the tungsten filaments, which results in increased light bulb life.

Argon is also used to create an inert atmosphere for growing semiconductor crystals, arc welding and for processes that need protection from other kinds of atmospheric gases.

Fe2O3 + 3CO = 2Fe + 3CO2

Hematite + Carbon Monoxide = Iron + Carbon Dioxide

In this reaction, the iron oxide is reduced to iron, and the carbon is oxidised to carbon dioxide.