When substances undergo changes, they can be categorized as either physical changes or chemical changes. Physical changes involve alterations in the appearance or state of matter without changing the chemical composition of the substance. For example, when ice melts into water, it is a physical change because the water is still H2O, only the physical appearance of the water changed. Another example is when you crumple a piece of paper - the paper changes its shape but remains paper. On the other hand, chemical changes result in the formation of new substances with entirely different properties than the original substance. One common example is the rusting of iron. When iron rusts, it combines with oxygen in the air to form a new substance, iron oxide, which has different properties than the original iron. The appearance of rust is evidence that a chemical change has occurred.
It's important to differentiate between physical and chemical changes because they have distinct characteristics and effects. By understanding the differences, we can better predict and explain the behavior of substances in various situations. Observing changes in matter and identifying whether they are physical or chemical changes helps scientists and chemists in analyzing reactions, developing new materials, and understanding the world around us. Next time you see a change happening, think about whether it's just a physical transformation or a chemical reaction taking place!
The following list includes evidence that you can look for after a change that indicates that a physical change may have occurred:
• change in size
• change in shape
• change in state (of matter)
The following list includes evidence that you can look for after a change that indicates that a chemical change may have occurred:
• unexpected change in color or odor
• formation of gas (bubbles or foam)
• formation of a precipitate (solid forms in a liquid)
• change in energy (change in temperature, light, sound)
Answer the following questions to determine your understanding of chemical and physical changes.
Question 1
(6 points)
Physical Chemical
In a __ change, the chemical bonds between atoms are broken and rearranged to form new substances.
A __ change is a change in the appearance or state of a substance without any change in its chemical composition.
When iron rusts, it undergoes a __ change because new substances are formed.
When ice melts, it undergoes a __ change because its state changes from solid to liquid.
The boiling of water is an example of a __ change because the state of the water changes from liquid to gas.
Cooking an egg is an example of a ___ change.
Question 2
The following chart lists examples of evidence that can be seen after a change has taken place. Use the information given previously to determine if the evidence supports a physical or chemical change occurring. (6 points)
Evidence of a Physical Change Evidence of a Chemical Change
Ash is present after a bonfire.
There is a sour smelling liquid present in a cup of milk that was left on the counter for 3 days.
A balloon is much smaller after letting the air out.
There is a loud sound after a firework explodes in the air.
There is a liquid substance in a pot after putting in a chunk of butter.
There is a brown banana on the counter that was originally yellow.
1 answer
Question 1
(6 points)
In a chemical change, the chemical bonds between atoms are broken and rearranged to form new substances.
A physical change is a change in the appearance or state of a substance without any change in its chemical composition.
When iron rusts, it undergoes a chemical change because new substances are formed.
When ice melts, it undergoes a physical change because its state changes from solid to liquid.
The boiling of water is an example of a physical change because the state of the water changes from liquid to gas.
Cooking an egg is an example of a chemical change.
Question 2
(6 points)
Ash is present after a bonfire. (Chemical Change) - The formation of ash indicates new substances have formed due to combustion.
There is a sour smelling liquid present in a cup of milk that was left on the counter for 3 days. (Chemical Change) - The sour smell indicates a chemical change due to the fermentation process.
A balloon is much smaller after letting the air out. (Physical Change) - This is a change in size without altering the air's chemical composition.
There is a loud sound after a firework explodes in the air. (Chemical Change) - The loud sound indicates a reaction has taken place, producing gases and possibly new substances.
There is a liquid substance in a pot after putting in a chunk of butter. (Physical Change) - This involves a change of state from solid to liquid without changing the chemical composition of the butter.
There is a brown banana on the counter that was originally yellow. (Chemical Change) - The change in color indicates a chemical change as the banana ripens and undergoes decomposition processes.
