Energy and Efficiency

Guys, guys I have a question, what is efficiency?

Well, efficiency can be described in several forms. But when we relate it with energy, we say that efficiency is the ability to produce a desired effect with minimum energy expenditure.

For example, which one uses less energy to cook a potato: A microwave or a normal oven. Of course the microwave uses less energy, thus we say it is more efficient than a oven. 

But let's put some math in this definition. Efficiency compares the input and output of energy. The ratio of useful energy produced (energy output) to energy used in its production (energy input), expressed as percentage. 

But what it energy output and input?

Energy output is the work done, energy delivered to consumer in usable form. You can find it by calculating Q=mc(tf-ti) or enthalpy change equation.

Energy input is the solar energy, fuel energy, power energy and etc. it is found through Hess' Law. 

LAB TIME:

To study energy efficiency, lets determine the efficiency of a barbecue why heat 5.10g of propane, and change the temperature of 250 g of water contained in a 500 g stainless steel pot (c=0.503 j/gxC) from 25C to 75C.

Well first of all lets find the energy output of this problem. By using Hess' Law we know that -236 kj.

Energy output can be figured by thermal energy equation which will give us a value of 65.0 kj

Now you take these two values, divide them and multiple by 100.