All Solutions
Section 5-1: Properties and Changes
Liquid nitrogen boiling at $-196text{textdegree}$ C is a physical change because only a change of state is taking place here.
Propane leaking from a damaged tank ignites easily is a chemical change as propane reacts with atmospheric oxygen to form carbon dioxide and water.
Equation:
$$
mathrm{C_3H_{8(g)} + 5O_{2(g)} longrightarrow 3CO_{2(g)} + 4H_2O_{(g)}}
$$
Silver jewellery tarnishes in air is a chemical change because the silver metal in the jewellery reacts with atmospheric air and water vapor to form tarnish.
Spilled oil generally floats on the surface of water is because of the physical property of oil to not mix with water and being less dense than water, it generally floats on its surface.
Meat darkens when heated on grill is because the meat in the presence of heat and flame undergoes a chemical change to get cooked.
Sulfur trixoide dissolves in water vapor of atmospheric air to form sulfuric acid. This is a chemical property of sulfur trioxide to form sulfuric acid.
Equation:
$$
mathrm{SO_{3(g)} + H_2O_{(g)} longrightarrow H_2SO_{_4(l)}}
$$
Air is often blended in ice cream to give it a lighter texture is a **physical** change where the ice cream mixture is beaten to allow air particles to become trapped in the mixture to decrease its density and give it its creamy texture.
Popping corns turn to pop-corns in the presence of heat is a **physical** change because the kernel pops and turns inside out. There is no new product formed.
The loud pop heard as a lit match extinguishes in a test tube containing hydrogen gas is because of a chemical reaction between hydrogen gas and atmospheric oxygen to form water. It’s a **chemical** change.
Equation:
$$mathrm{2H_{2(g)} + O_{2(g)} longrightarrow 2H_{2}O_{(g)}}$$
Ethanol is used to power vehicles as an alternate source of energy because ethanol in the presence of heat reacts with atmospheric oxygen to release energy and form carbon dioxide and water. This is a **chemical** reaction.
Equation:
$$mathrm{C_2H_{5}OH_{(l)} + 3O_{2(g)} longrightarrow 2CO_{2(g)} + 3H_2O_{(g)}}$$
Geothermal energy is used to power turbines to produce electricity. This is a **physical** reaction where the heat from the earth is used to change the state of water to steam and drive turbines to produce electricity.
The green stain of silver rings is the tarnish of silver. This is produced when silver chemically reacts with atmospheric air. It’s a **chemical** change.
The solvent used for this purpose should have a high solubility to easily dissolve paint. It should have a low boiling point. This physical property of the solvent will allow it evaporate and hence dry quickly. It should be unreactive to atmospheric air to prevent any chemical reaction from taking place.
Ideal solvents should have high solubility.
$1$. The material used for dental braces should be flexible to easily fit in the tight dental space.
2. It should also have a high melting point to remain in solid form in the warm environment of the mouth.
The material used for dental braces should be chemically inert to avoid any reaction with the wet (as well as low and high pH) environment of the mouth.
