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Chapter 6 Section 1:
Observing Chemical Change
◦Matter can be described in terms of physical and chemical changes
Property and changes of matter
A physical property is a characteristic of a substance that can be observed without changing the substance into another substance
Melting pt, boiling pt, color, hardness, texture, luster, ductility, malleability, conduction of heat and electricity
A chemical property is a characteristic of a substance that describes its ability to change into another substance(s).
Reactivity to Oxygen, burning/ flammability, tarnishing, and rusting
See figure 1, page 185
◦A physical change is any change that alters the form or appearance of a substance but it does not make the substance change into another substance
Bending, crushing, breaking, cutting
◦A chemical change is when the substance itself changes into another substance. This is called a chemical reaction.
Burning
Chemical changes occur when bonds break and new bonds form
◦Involve the formation of a new substance and changes in energy. Figure 4, page 188
Evidence for Chemical Reactions
Changes in properties result when new substances form
A solid that forms from a solution during a chemical reaction is called a precipitate
Color change
A gas might be produced
◦Matter can either absorb or release energy in the form of heat, light, electricity
Changes in energy
Occurs during chemical reactions
◦A change in temperature indicates absorption or release of energy
Endothermic: energy is absorbed, temperature does not always result in a decrease. Energy must continuously be added to have endothermic reactions (Bonds are being broken, energy is needed)( Takes energy from surroundings)
Ammonium thiocyanate is mixed with barium hydroxide.
A drop of water is placed on a block of wood.
The bottom of the beaker becomes cold enough to freeze the water and stick to the wood.
Exothermic: energy is released as heat so the temperature increases
(Bonds are being formed, have more energy than needed)
(Heat given to surroundings)
