What you have is a good idea, but it's not a good definition. You can start, as you mention, by saying that in its simplest form work is force times distance. I like to work a few simple examples and then do a demonstration or two that shows how a simple machine can reduce the force, but only at the expense of increasing the distance, thus the utility of the concept of work. From there you can refine the concept of work by considering forces that are not parallel to the displacement, and forces that are not constant, to whatever extent you deem appropriate for the level of your presentation.
Note that you don't need to define energy, but it is useful to do as you suggest and stress that whenever work is done energy is being transferred. You can also mention that the other way to transfer energy is heat, but if you do that I recommend an in-depth discussion of processes that involve a temperature change with no heat, and vice versa.
The article by Arons, Am. J. Phys. 67, 1063 (1999), is an excellent source of information.
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From: Phys-l on behalf of Philip Keller
Sent: Tue 29-Oct-13 10:48 AM
To: Phys-L@phys-l.org
Subject: [Phys-L] defining energy
Hello,
I am going to be teaching this topic to my 11th graders soon. I have a
question about the definition of energy. I know that the "ability to do
work" definition runs into trouble when you consider heat, engines and 2nd
law issues. But what if I turn the definition around. Instead of saying
"energy is the ability to do work", I want to say:
Work is defined to be the product of force and displacement (in the same
direction). Then, in different contexts, you can show that work = delta
(some quantity). Any such quantity is referred to as [blank] energy. Fill
in the blank with an adjective that fits the context.
So "energy" is not the ability to do work, but energies are the quantities
that are changed by work.