The cathode reaction in the Leclanch cell is given by 2MnO2(s) 1 Zn21(aq) 1 2e2 ZnMn2O4(s) If a Leclanch cell produces a current of 0.0050 A, calculate how many hours this current supply will last if there are initially 4.0 g of MnO2 present in the cell. Assume that there is an excess of Zn21 ions.

General Chemistry 1305 Week 2 Notes 1.Dimensional Analysis 1.1 Units of Measurement Quantities and measurements made in the lab or elsewhere have a numeric value, however, this numeric value is meaningless unless it’s followed by a unit which relates the number to a certain property or measurement. Currently there are two main unit systems, the American system and the SI (Systeme International) which is widely accepted in all sciences. The SI units are: Volume : Volume is the amount of three-dimensional space a 3 substance occupies. cubic meter (m ). Mass: Mass is the amount of matter in a substance. the SI unit is the kilogram (kg). Length: the SI unit is the meter (m). Temperature: is a measurement of the kinetic energy of molecules inside a sample. The more motion that occurs, the higher the temperature. While Americans use Faranheit and the rest of the world uses Celsius, the SI unit for temperature is Kelvin (K). Because measurements and calculations give results that vary from really small numbers to huge ones, a system exists to help express these values: 1.2 Scientific Notation As well as prefixes, scientific notation is method to easily express small and large numbers. Numbers expressed with scientific notation have the following format: 500.00= 5.00000*10^2. (example of a number greater than 1), 10 is squared which means the decimal point is moved two places to the right. 0.005