Matter and Energy

Energy is the capacity to do work.Physical changes such as boiling, freezing

and evaporation involve energy changes.Chemical changes involve chemical reactions

which all involve energy changes.An endothermic reaction describes a process

in which energy is absorbed.An exothermic reaction describes a process

in which a system releases heat into the environment.

The law of conservation of energy states that energy cannot be created or destroyed but can be changed from one form to another.

Conservation of Energy

Heat vs. Temperature

Heat is the energy transferred between objects that are at different temperatures. HEAT IS THE TOTAL KINETIC ENERGY.

TEMPERATURE IS THE AVERAGE KINETIC ENERGY.

Kinetic energy (KE) = ½ mv2 where m is mass and v is velocity.

What has more heat content a cool swimming pool or a cup of boiling water?

Other energy types and temperature scalesPotential energy is stored energy and can

include gravitational (gPE = mgh), mechanical, and chemical.

Temperature can be measured in Fahrenheit (oF), Celcius (oC), or Kelvin (K, no degree symbol).

oC = oF – 32*5/9 OR oC = oF + 40*(5/9) -40oF = oC*9/5 + 32 OR oF = (oC + 40)*(9/5) – 40K = oC + 273.15oC = K – 273.15

Specific heatSpecific heat is the quantity of heat required

to raise the temperature of a unit mass of homogeneous material 1 K or 1 oC.

Units can be J/g oC, J/g K, KJ/Kg K, etc.

Heating curve for water

Scientific method

Scientific method cont.Accidental discoveries (3M, Teflon, sticky

notes, etc).An experiment must have a control (a

comparison).Variable types: independent variable –

you choose this in an experiment, dependent variable – you measure this in an experiment, discrete – a counting variable, and continuous – a measurement variable.

Measurements and Calculations in Chemistry Accuracy – the closeness to the true or

accepted value.Precision – the repeatability of a

measurement.Good measurements are both accurate and

precise.

Significant figures (digits)Nonzero digits are always significant.Zeros between nonzero digits are

significant. Example 303 has 3 significant digits.

Zeros to the RIGHT of the decimal are significant if there is a significant digit TO THEIR LEFT. .003 has 1 while .0030 has 2.

Zeros to the LEFT of the decimal are significant if there is a significant digit TO THEIR RIGHT. 300 has 1 while 300.0 has 4.

Scientific notation can be used to make zeros significant for the cases above. If 300 should have 3 instead of 1 write it as 3.00 x 102

Practice!List how many significant digits in the following:400

56,000.0

0.00045

0.000006500

5050

3.900 x 10 -7

Rules for using significant figures in calculationsIn using multiplication and division, the

answer can have no more significant digits than the least number in the measurements.

For addition and subtraction the final answer goes by the least number of decimal points in the measurements rather than significant digits.

Scientific notation review and calculator useConvert 53400000 to scientific notation

Convert 0.0000098040 to scientific notation

Calculate this (correct sig figs):(3.89 x 106)(5.400 x 10 -8)÷ ( 1.9999 x 1014)(3.89 x 106)(5.400 x 10 -8)/(1.9999 x 1014)

Now try this:(7.63 x 103)( 6.023 x 1023)/(8.6023 x 10 -4)

Remember denominator, divideUse the EE or exp key to enter the x 10