Changes to Matter

Changes to Matter

Multiple Choice

Going from the trees to the firewood represents which kind of change?

• physical change

• chemical change

Physical Change

The re-arrangement of existing particles in a substance or material.

New substances are NOT formed.

(Composition remains the same)

Physical Changes

due to applied force

• Cutting

• Chopping

• Crushing (powderizing)

• Grinding

• Breaking

• smaller pieces = more surface area, but not new substance(s)

Physical Changes
due to Heat in or out

(phase changes)

• melting (s) --> (l)

• vaporizing, (l) --> (g)

• subliming, (s) --> (g)

• condensing, (g) --> (l)

• freezing, (l) --> (s)

• depositing, (g) --> (s)

​Water on a hot plate

At the particle level

Multiple Choice

True or False,

As water evaporates, a new substance is created.

• True

• False

False

Changing phase from liquid to gas does not change a water molecule into a new substance. (Still H₂O)


H₂O (l) --> H₂O (g)

Dissolving is considered a physical change!!

Ex: dissolving solid NaCl in water

NaCl _(s) ---> NaCl <sub>(aq)


NaCl (s) can be recovered using physical methods of separation</sub>

Multiple Choice

Which of the following is NOT a physical change to matter?

• a beaker of water is now empty after sitting out for all summer

• ice cream begins to drip down the side of the cone

• vinegar is poured on baking soda and bubbling occurs

• a sugar cube is dissolved in water

Answer: Baking soda + vinegar

A new substance (CO₂) is formed that has different composition than the original substances (NaHCO₃).

A chemical reaction occurred.

(a.k.a. a chemical change)

Open Ended

Prior Knowledge:

What kinds of observations would indicate to you that a chemical change occurred?

(i.e. what would you notice with your senses?)

Chemical Changes

The formation of new substances with physical and chemical properties different than the starting substances.

Chemical composition has changed (chemical formula is different now)

Signs of Chemical Change:

Change in Temperature

• Most chemical reactions release heat

• (though a few absorb heat)

• If Temp goes up, heat was released. (exothermic)

• If Temp goes down, heat was absorbed. (endothermic)

​combustion of a fuel (such as propane)

Signs of Chemical Change:

Color Change

• Example: Some compounds change color based on acidity of the solution

Signs of Chemical Change:

Light released

• some chemical reactions release energy in the form of light

Signs of Chemical Change:

Formation of a precipitate

• PbCl_{2 (aq)} + 2NaI _(aq) ---> PbI_{2 (s)} + 2NaCl _(aq)

Signs of Chemical Change:

Formation of a gas

• Ex: Alka Seltzer tablet in water

• production of CO_{2 (g)}

Signs of Chemical Change:

Production of NEW Odor or Flavor

• Cooking causes chemical changes in foods that are observed as new smells or new flavors

• Examples: carmelizing onions, baking bread

Multiple Select

Select all that apply.

Which could indicate a chemical change took place?

• A color change occurs when 2 liquids are mixed

• a blue flame is seen above a liquid after a spark

• You apply heat to a liquid and bubbles form under the surface

• gas bubbles form after placing a piece of metal into acid

Recap Slide 1

Physical changes alter the arrangement of particles, but do NOT change the composition:

• cutting, crushing, powderizing (more pieces and surface area)

• phase changes NaCl (s) --> NaCl (l)

• dissolving NaCl (s) --> NaCl (aq)

Recap Slide 2

• Chemical changes result in new substance(s) with different properties than the starting materials.

• Ex: 2Na _(s) + Cl_{2 (g)} ---> 2NaCl _(s)

• Sodium metal and chlorine gas are the "reactants" (starting materials)

• Sodium chloride is the "product" and has different properties than the reactants

Recap Slide 3

Signs of a chemical change include:

• Spontaneous formation of a gas (bubbling), solid precipitate, or new odor/taste

• release of light

• Temperature change (Heat change)

• Color change

be sure you have key definitions, and examples in your notes