Problem Solving One of the most important things
Problem Solving • One of the most important things we do in life is solve problems. • The more creative we are at solving problems, the more successful we will be. • It is helpful to use the following steps when solving a problem.
Where Do We Want To Go? • To solve a problem, we need to be able to state the problem clearly. What Do We Know? • This represents the starting point. How Do We Get There? • How do we use the facts we know and the understanding we have of the relevant concepts to proceed from the starting point to the eventual goal – the solution to the problem.
Does It Make Sense? • After we have reached the solution, we need to evaluate it. Is the answer we have obtained reasonable? Converting Units of Measurement • This is something you encounter all the time: converting from one unit of measurement to another. Where Do We Want To Go? • 2 dozen doughnuts = $?
What Do We Know? • 1 dozen = 12 • 1 doughnut =$0. 50 How Do We Get There? • Convert dozens of doughnuts to numbers of doughnuts then to cost of doughnuts: 2 dozen doughnuts → numbers of doughnuts →cost of doughnuts
• We can make each of these conversions as follows: • The doughnuts will cost $12. Does It Make Sense? • The answer $12 seems reasonable. First, the units are correct and each doughnut costs less than $1 so we should have an answer less than $24.
Conversion Factors • Ratio derived from the equality between two different units that can be used to convert from one unit to another. • Example: 4 quarts in 1 gallon
Which conversion factor should be used to convert from gallons to quarts? Let’s convert 0. 75 gallons to quarts. 4 quarts = 3. 0 quarts 0. 75 gallons x 1 gallon
• Changing from one unit to another via conversion factors (based on the equivalence statements between the units) is often called dimensional analysis. • We will use this method throughout our study of chemistry.
TEMPERATURE CONVERSIONS • Three scales: Fahrenheit scale, Celsius scale, and Kelvin scale. • Fahrenheit scale: water boils at 212 o. F and freezes at 32 o. F and normal body temperature is 98. 6 o. F. Used widely in the US and Great Britain. Named after Daniel Gabriel Fahrenheit.
• Celsius scale: water boils at 100 o. C and freezes at 0 o. C. Named after Anders Celsius. • On both the Celsius and Fahrenheit scales, the unit of temperature is called a degree, and the symbol for it is followed by the capital letter representing the scale. OF and o. C
• Kelvin scale: water freezes at 273 K and boils at 373 K. The unit of temperature is called a kelvin and is symbolized by K. Named after William Thomson, who received the title, Lord Kelvin. • The size of each temperature unit (each degree) is the same for the Celsius and Kelvin scales. • The Fahrenheit degree is smaller than the Celsius degree and the Fahrenheit unit. • The zero points are different on all three scales.
Converting Between the Kelvin and Celsius Scales TCelsius + 273 = TKelvin Converting Between the Fahrenheit and Celsius Scales
• Density is a characteristic physical property of a substance and can be used for identification. • Density is the ratio of mass to volume, or mass divided by volume (D = m/v). • The SI unit for density is kg/m 3. In the lab you will usually see density expressed as g/m. L or g/cm 3.
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