CHEMISTRY COMMUNITY

I'm having trouble determining when to use the equation E=hc/wavelength. I understand what the constants are h (Plank's), c (speed of light), and wavelength, but I'm not entirely sure how to implement it. What makes this equation better than using E=frequency*h or c=wavelength* frequency? To be completely honest I'm getting all of these equations mixed up please explain them.

Hi Isabelle,
These various equations are used for finding different things. For example if you are asked to find the energy you can not use c= wavelength*frequency, because in this case energy is not even in the equation given. If you are asked to find energy you should use one of the other two equations, you can determine which to use based on the information given to you. If you are given just wavelength and are trying to find energy, it would be best to use E=hc/wavelength. If you are given frequency and not wavelength and you want to find wavelength it would be good to use c=wavelength*frequency. So basically, it is all dependent on the information that is given to you. The best advice I can give you is to look at your givens and be manipulative! Use whatever works best for the SPECIFIC problem you are working on.

Sorry this is off topic but do we have to memorize these two equations or is it going to be given to us?

so we can use these equations interchangeably for one another right?

I am very sure we would be given a formula sheet in front of the exam. A good way to check which formulas are on the formula sheet go to the class website and click constants which is one below everything you want to know about sig figs. Even though the formulas are given, it is very advisable to remember the formula as it would help you go through the test with ease without flipping back and forth.

Also to explain E=hc/wavelength. E=hc/wavelength comes from the c=frequency times wavelength. When you experiment with the equation and you get frequency equals speed of light/ wavelength since E=h(frequency). Therefore you would get E=hc/wavelength.

I hope this helps. Correct me as I might be wrong in some places.

Jocelyn1B wrote:Sorry this is off topic but do we have to memorize these two equations or is it going to be given to us?

Hi Jocelyn! These equations as well as constants will be given on the test!

A lot of times we will use multiple equations to solve one problem so we might use what is given in one equation in order to plug that answer into the other equation.