Matter & Energy

Ch.2

(2-1) Chemical E

• E that exists in the bonds that hold atoms together

• When bonds are broken chemical E is released– Digesting food

Energy

• The capacity to do work

• SI unit: joule (J)

• Law of conservation of E: E is neither created nor destroyed– Einstein: If matter is destroyed, E is

created. If E is destroyed, matter is created. So the total amt of mass and E is conserved.

Mass & E Are Closely Related

• E = mc2

• Relates how much E can be obtained from a given mass

Types of E

• Kinetic (KE): E in motion– The faster an object moves the more KE it

has– Depends on mass and velocity– KE = ½ (mv2)

• Potential (PE): E of position– Stored E

E Can Be Transferred

• Heat: sum total of KE of the particles in a sample of matter

• System: all components that are being studied – Surroundings

Temperature

• Measure of the avg. KE of the particles in a sample of matter

Temp. Scales

• Kelvin(K) = ºC + 273.15 ºC– Absolute zero: lowest temp. theoretically

• Celsius (ºC) = K – 273.15 K = (ºF – 32) x 5/9

• Fahrenheit (ºF) = (ºC x 9/5) + 32

Specific Heat Capacity

• (cp): amt. of heat E required to raise the temp. of 1 g of a substance by 1 K

• Units: J/g•K

• Calculated from experimental data

(2-2) Scientific Method

• Observe• Form hypothesis

– Testable explanation of observations– If, then

• Test– Controlled experiment

• Theorize– Well-tested explanation of observations

• Publish results

Scientific Law

• Description of the natural world that has proven reliable over time– Describes, doesn’t explain

• Law of conservation of mass: mass is neither created nor destroyed

(2-3) Measuring

• Accuracy: how close it is to true value

• Precision: how closely several measurements are to 1 another– Can be precise w/out being accurate

Significant Figures

• Any digit that’s known w/ certainty plus 1 final digit

• Nonzero digits are always significant

• See Table 2-3, p. 59

Sigfig Rules for Zeros

1. B/w nonzero digits are- 40.7 has 3 sigfigs

2. In front of nonzero digits are not- 0.009587 has 4 sigfigs

3. At end of # and to right of decimal are- 85.00 has 4 sigfigs

4. At end of # with no decimal may or may not be

- 2000 can have 1 to 4; 2000. has 4 sigfigs

Exact Numbers

• 2 types:– Count

• 24 students in Chemistry

– Conversion factor • 1000 mm in 1 m

• Unlimited # of sigfigs (no uncertainty)

Calculations

• x & ÷: smallest # of sigfigs

• + & -: smallest # to the right of decimal

Calc. Practice

• 12.257 x 1.162 = 14.2426234– 4 sigfigs = 14.24

• 3.95 + 2.879 + 213.6 = 220.429– 1 place = 220.4

Scientific Notation

• Used for very large or very small numbers

• 1st part: # 1 to 10

• 2nd part: power of 10

• Ex: 0.000 000 000 000 005 = 5 x 10-15

• Ex: 1 000 000 000 = 1 x 109