evidence of physical and chemical change
The formation of the gas may indicate that a chemical reaction has taken place. For example when vinegar is added to baking soda, it forms carbon dioxide bubbles.
Butter melting, paper shredding, glass breaking
PHYSICAL CHANGE
CHEMICAL CHANGE
When solid or liquid substances are combined, they may form gas bubbles.
The precipitate may be in the form of very small particles, appearing as cloudiness in the solution or as a solid which settles to the bottom of the container.
When a substance changes from one state of matter to another (for example, changing from solid to liquid, from liquid to solid, or from liquid to gas), the composition of the substance remains the same.
When a substance changes color, the chemical composition of the substance may have changed (for example, iron turns to a reddish-brown when it rusts, apples brown when they react with oxygen in the air, or marshmallows turn black when burned).
When a substance changes directly from a gas to a solid (the forming of frost from water vapor) or from a solid to a gas (dry ice, solid air fresheners) that change of state is called sublimation. This is still a physical change because the composition of the substance remains the same.
When a substance is combined with another substance, there may be an increase or decrease in temperature (for example, when wood burns to ash and gases, the temperature increases.
Examples of change in size or shape might include: shredding paper, dissolving sugar in water, stretching a rubber band, wadding up a piece of paper, or denting a piece of metal.
When two solutions are combined, they may form a solid substance. This solid substance is called a precipitate and indicates that a chemical change has occurred.
When a substance changes in size or shape (for example, cutting, tearing, dissolving, stretching, or wrinkling), its composition remains the same.
NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2
do not change the composition of a substance, only the physical properties
For example when carbon dioxide is combined with aqueous calcium hydroxide (limewater), solid calcium carbonate (chalk) is formed as the precipitate.
Examples of change in state might include: melting of ice cream, hardening of melted wax, or evaporating of water from wet clothes.
It is possible to have a color change without a chemical change (for example, adding food coloring to water)
