Chapter 2 Matter & Energy
2-1 What is Energy? Energy is the capacity to do work Potential Energy: energy due to position Kinetic energy: Energy due to motion How does this relate to chemistry? Motion of matter (vibrate, flow or collide) Stored energy in bonds When the bonds are broken, energy is either released (exothermic) or absorbed (endothermic).
2-1 What is Energy? Law of Conservation of Matter Matter can not be created or destroyed, it only changes form
2-1 What is Energy? System is a piece of universe we are studying
2-1 What is Energy? Temperature is a measure of the average kinetic energy of particles in a substance. Misconception: temperature is NOT how hot or cold something is. Use the Kelvin scale in science – absolute zero To convert from oC to K K = oC + 273 oC = K - 273
2-1 What is Energy?
2-2 What is the Process of Science?
2-2 What is the Process of Science? Hypothesis – reasonable and testable explanation of observations Theory – well tested explanation of observation (results are easily reproducible) Scientific Law – description of the natural world that has proven reliable over time
2-3 How do Chemists Measure Quantities? Accuracy is how close a value is to the correct or accepted value. Precision is how close a series of measurements are to each other. Why are both accuracy and precision important in the lab?
2-3 How do Chemists Measure Quantities?
2-3 How do Chemists Measure Quantities? Significant figures are important when we measure something. It tells us how accurate our tools are. When an object is measured there is always a degree of uncertainty in the last value because it is always an estimated value.
2-3 How do Chemists Measure Quantities? Any non zero digit is significant. Zeros between significant figures are significant. Zeros at the end of a number and to the right of a decimal are significant. Zeros in front of non zero digits are not significant. Zeros at the end of a number with no decimal are not significant.
2-3 How do Chemists Measure Quantities? Used to write very small or very large numbers (easier to write and less likely to make mistake by leaving off or adding extra zeros) Rules If number is greater than 1, you have a positive exponent. (move decimal to the left to create number between 1 and 9.9) If number is less than1, you have a negative exponent. (move decimal to the right to create number between 1 and 9.9)