2. Which of the following are chemical changes?
a. mercury has a density of 13600 kg/m3
b. potassium reacts with water
c. hammer a nail into a piece of wood
d. a rotting apple
e. potassium is a soft metal
f. evaporation of water g. sublimation of dry ice
h. dissolve sugar in water
i. a growing flower
j. hydrogen is a flammable gas
b. potassium reacts with water
d. a rotting apple
f. evaporation of water
g. sublimation of dry ice
h. dissolve sugar in water
i. a growing flower
j. hydrogen is a flammable gas
To determine which of the following are chemical changes, we need to identify if a chemical reaction is taking place. Chemical changes involve the breaking and forming of chemical bonds, resulting in the creation of new substances. Now let's evaluate each option:
a. Mercury has a density of 13600 kg/m3: This is a physical property of mercury and does not involve a chemical change.
b. Potassium reacts with water: This is a chemical change as it involves the reaction between potassium and water, resulting in the formation of potassium hydroxide and hydrogen gas.
c. Hammer a nail into a piece of wood: This is a physical change as it involves the change in the position and shape of the nail and the wood, but no new substances are formed.
d. A rotting apple: This is a chemical change as the process of rotting involves the breakdown of organic matter through the action of enzymes and microorganisms, resulting in the formation of new substances.
e. Potassium is a soft metal: This is a physical property of potassium and does not involve a chemical change.
f. Evaporation of water: This is a physical change as it involves the conversion of liquid water to water vapor, but no new substances are formed.
g. Sublimation of dry ice: This is a physical change as it involves the direct conversion of solid dry ice (carbon dioxide) to carbon dioxide gas, but no new substances are formed.
h. Dissolve sugar in water: This is a physical change as it involves the sugar molecules dispersing in water, but no chemical reaction takes place.
i. A growing flower: This is a complex biological process involving the uptake of nutrients and water, as well as the synthesis of new molecules, making it a chemical change.
j. Hydrogen is a flammable gas: This is a physical property of hydrogen and does not involve a chemical change.
Therefore, the options that involve chemical changes are:
- Potassium reacts with water (b)
- A rotting apple (d)
- A growing flower (i)
To determine which of the given scenarios are examples of chemical changes, we need to understand what a chemical change is.
Chemical changes involve the formation or breaking of chemical bonds, resulting in the formation of entirely new substances with different chemical properties. This is usually accompanied by a change in the physical properties of the materials involved, such as color, odor, temperature, or the production of gas.
Let's go through each scenario to analyze if it involves a chemical change:
a. Mercury has a density of 13600 kg/m^3 - This statement is about a physical property of mercury and not related to any chemical changes.
b. Potassium reacts with water - This is a chemical change because potassium reacts with water to form potassium hydroxide and hydrogen gas.
c. Hammer a nail into a piece of wood - This is a physical change as it involves a change in shape or position but does not result in the formation of new substances.
d. A rotting apple - This is a chemical change. The decomposition of the apple involves the breakdown of its organic compounds, such as sugars, resulting in the formation of new substances and changes in color and odor.
e. Potassium is a soft metal - This is a statement about a physical property of potassium and does not involve any chemical changes.
f. Evaporation of water - This is a physical change. When water evaporates, it changes from a liquid state to a gaseous state, but the water molecules remain the same.
g. Sublimation of dry ice - This is a physical change. Dry ice, which is solid carbon dioxide, sublimates directly from its solid state to its gaseous state without forming new substances.
h. Dissolve sugar in water - This is a physical change. Sugar dissolves in water to form a sugar-water solution, but the chemical composition of sugar remains the same.
i. A growing flower - This is a complex process involving both chemical and physical changes. The growth of a flower involves the uptake of water and nutrients and the production of new cells, which are chemical changes.
j. Hydrogen is a flammable gas - This is a statement about a physical property of hydrogen and does not involve any chemical changes.
In conclusion, the following scenarios involve chemical changes:
- Potassium reacts with water.
- A rotting apple.
- A growing flower.
It is important to note that while some scenarios may involve both physical and chemical changes, the ones mentioned above have significant chemical changes taking place.