1B3 :  Units and Carbon Dioxide Emissions  4 pts 

A new, energyefficient home refrigerator consumes about 350 kWh of electricity per year. Assume the electricity is generated by burning fossil fuels. When fossil fuels like coal, oil, natural gas and gasoline are burned, most of  
the carbon in the fuel burns completely to form carbon dioxide (CO_{2}). CO_{2} is a greenhouse gas that contributes to global warming and that is undesirable. In a typical natural gas power plant, 0.5 kg of CO_{2} is produced for each  
kWh of electricity generated. Consider a city with 500,000 homes with one refrigerator in each home. How much CO_{2}, in metric tons, is produced by the refrigerators in the city in one year?  
Read:  This problem is all
about unit conversions. Keep careful track of units and it will not be difficult. A kWh is unit of energy. A Watt is energy per time and when you multiply by hours (time) you are left with units of energy. A kWh is kW times hours. It is the amount of energy consumed in an hour by a device that uses 1 kW of power (1 kJ/s for 3600 sec). 

Given:  m_{CO2}  0.5  kg CO_{2} / kWh  Power  350  kWh/house/year  
N  500000  houses  
Find:  M_{CO2}  ???  mton CO_{2} / year  
Assumptions:  None.  
Equations / Data / Solve:  
The total mass of CO_{2} produced per year is the product of the rate of CO_{2} production per kWh, the rate at which power is used by each house and the number of houses.  

Eqn 1  
Check the units in this equation :  

Eqn 2  
Plug in the values :  M_{CO2}  8.75E+07  kg CO_{2} / year  
Unit conversion factor :  1 metric ton =  1000  kg  
Therefore :  M_{CO2}  87500  mton CO_{2} / year  
Answers:  M_{CO2}  87500  mton CO_{2} / year 