Answer to Question #249639 in General Chemistry for Anna

Question

Identify whether the following processes are endothermic or exothermic.

1. Thermal decomposition of limestone to form calcium oxide (CaO) and carbon dioxide
2. Explosion of a firecracker triggered by a spark
3. Combustion of hydrogen gas
4. Dissolving an acid in water
5. Baking bread
6. Heating causes sodium bicarbonate (NaHCO₃) to decompose

Answer 1

1. limestone,CaCO3(s) decomposed into calcium oxide,CaO and carbon dioxide,CO2.

It is necessary to heat limestone to a high temperature for this reaction to occur. CaCO3(s) + heat → CaO(s) + CO2(g)

So, it is a endothermic reaction

2. Explosion of a firecracker triggered by a spark leads to produce lots of heat , So it is definitely a Exothermic reaction.

3. Combustion of Hydrogen gas (H2) produce H2O and heat is produced in this combustion.

2H2 + O2 → 2H2O + heat

So it is a Exothermic reaction.

4. On dissolving an acid in water, H+ iones and it's anionic counter part becomes solvated by water and heat is produced in this solvation process.

E.g. H2SO4 + water → 2H+(aq) + SO4 2-(aq) +heat

So it is a Exothermic reaction

5. The flour, yeast, and other ingredients used in creating the dough are heated. They absorb the heat and chemical reactions happen. i.e. Baking of bread occurred.

So, as they use heat in the reaction it is a endothermic reaction.

6. Heating causes sodium bicarbonate (NaHCO3) to decompose as follows

2NaHCO3(s) + heat → Na2CO3(s) + H2O(g) + CO2(g)

As heat is used in this reaction it is a endothermic reaction.