Chapter 2

More chem – Less math

The Scientific Method

How do scientists do what they do?

Can this method be applied to everyday life?

The scientific method is an approach to problem solving.

It is a general strategy to provide a sound conclusion.

At its most basic, the SM can be thought of as:

Question → Possible answer → Test

Publishing – sharing results

Hypothesis-possible hypothesis –

possible answerans explanation

Experiment-testing hypothesis

Conclusions

Observation or question

Conclusions from an experiment may lead to: Scientific Law – A description of something in

nature. This may take the form of an equation.Examples:

Scientific Theory – An explanation for something in nature supported by data.Examples:

Model – A representation of something in nature.Examples:

Experimental Control – Controls are used in experiments to give a basis of comparison or a baseline reading.Essentially, it answers the question, “What happens if I do nothing?”

Examples:

Serendipity

Unexpected or unintended, but beneficial outcome of an experiment.

Roentgen - Discovered X-RaysP. Spencer – Microwave useA. Fleming – Found penicillinTeflon – Searching for refrigerants

Accuracy and Precision

Descriptions of experimental data

The Accuracy of experimental data indicates how well the data agree with known values.(How close to the bulls-eye).

Ex: The actual mass of a beaker is 250.0 g. You measure the mass to be 249.2 g. Your accuracy would be good.Your partner measures the mass as 225.7 g – poor accuracy

The Precision of experimental data indicates how consistent the data is. (How close the darts are to each other)

Ex: You weigh the beaker 3 times and get 249.2, 259.4 and 238.8g. – Precision is poor. (But average accuracy is good)

Your partner measures 225.7, 225.9, 226.0 g. –Precision is good – but accuracy is still poor. What is the mass of the beaker?

Energy Considerations

In general, energy must be transferred or transformed during any chemical or physical change.

The Law of Conservation of Energy says that energy cannot be created or destroyed in any chemical or physical change.

In a chemical reaction, the total amount of energy must be the same on both sides of the equation.

System – The reaction, process or object under study.Surroundings – The rest of the universe.Energy lost by one must be gained by the other and

vice-versa!!Closed system – energy cannot leave or enter the

system.Open system – energy is exchanged between system

and surroundings.Examples:

Kinetic energy – energy due to the motion of an object.

Potential energy – energy due to the relative positions of objects!!!

Forming chemical bonds releases energy

Breaking bonds requires energy.

Exothermic - Energy released to surroundings

Endothermic - Energy absorbed from surroundings

Chemical energy is the energy in matter due to chemical make-up. Can be thought of as stored in bonds.

Heat and Temperature

Heat can be described as the total amount of kinetic energy contained by a sample of matter.

See Java

Temperature is a measure of the average amount of KE of the particles of a sample of matter.

50oC

100oC100oC

What if they were filled with money rather than water?$50 bills $100 bills

Specific Heat Capacity

• 2014 -omit

Temperature Scales

Fahrenheit – 1724 – Commonly used in US. Based on freezing point of brine and “blood temperature”

Celsius – 1742 – Anders Celsius. Developed by many scientists. Based on freezing and boiling point of pure water. Known as centigrade until 1948.

Kelvin – Lord Kelvin (W. Thompson) 1848. Calculated as temperature where a gas has zero volume. Same size “degree” as Celsius.

Conversions

K = C + 273

(F+40)5/9 = (C+40)

Or

F=1.8 C +32 C= 0.56 (F-32)

Practice:

Average human body temperature is 98.6 oF. What is this temp in C and K?

Lead (Pb) has a melting point of 327 oC. What is this temp in F and K?

Nitrogen (N) boils at 77 K. What is this temp in C and F?