Question

Question 19
One molecule of Iodine (I2) and two molecules of sodium chloride (NaCl) combine in a reaction. How many atoms are in the products?

a
4
b
6
c
3
d
2
Question 20
Which event is an example of an exothermic reaction?

a
decomposition
b
melting ice
c
evaporation
d
combustion

Answer 1

**Question 19:** In the reaction between one molecule of iodine (I₂) and two molecules of sodium chloride (NaCl), we can count the atoms in the products.

- One molecule of I₂ contains 2 iodine (I) atoms.
- Two molecules of NaCl contain 2 sodium (Na) atoms and 2 chlorine (Cl) atoms (since each NaCl contains 1 Na and 1 Cl).

Now, let's count the total number of atoms in the products:
- From I₂: 2 I atoms
- From 2 NaCl: 2 Na atoms + 2 Cl atoms = 4 atoms

Total number of atoms = 2 (I) + 2 (Na) + 2 (Cl) = 6 atoms.

**Answer: b** (6)

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**Question 20:** An exothermic reaction is one that releases energy, usually in the form of heat.

Looking at the options:
- **a) Decomposition**: This can be endothermic or exothermic; it depends on the specific reaction.
- **b) Melting ice**: This is an endothermic process because it absorbs heat to change from solid to liquid.
- **c) Evaporation**: This is also endothermic, as it requires heat to change liquid to gas.
- **d) Combustion**: This is a classic example of an exothermic reaction, as it releases heat and light when a substance combusts.

Thus, the correct answer for an example of an exothermic reaction is:

**Answer: d** (combustion)