Chemistry homework problems on Enthalpy. HELP!!?

Question

1. what is the difference between change of energy vs. change of heat?
2. why is enthalpy so change of heat?
3. what is the difference between heat and enthalpy?
4. what are standard conditions?
5. What is change in Hf? How do you use it?
6. what so change of H rnx is?
7. change of energy = q +w what does this mean? what's q? how does this relate to change in qw
8. What is pressure volume work?
9. What si teh difference between work and energy?
10. Why enthalpy not heat? why is Kelvin used?

If you can answer some of these questions that would be awesome. thanks

Answer 1

I'll answer a few of these to get you started.

1.) Heat is only one type of energy. If, for example, you just heat something up or cool it down, then there is just a change in heat. But if there is a reaction, then there is a change of energy without a change of heat.

3.) Enthalpy is defined as the thermodynamic potential of a system, which means that it's a function of heat, pressure, and volume, not just heat.

4.) Standard conditions: Usually Standard Temperature and Pressure, meaning 0C and 100 kPa.

7.) Q = energy added by heat. W = work. Thus, the internal energy of a system is dependant on both the heat and the work done on a system. For example, you could heat a gas, or you could simply compress it (lowering volume, increasing pressure) - both of which would increase the internal energy of the system.

8.) Related to 7: Changing the pressure and volume of a gas will do work upon it.

9.) Work is a form of energy - it's the actual mechanical work that can be achieved when energy is expended. In an ideal system, energy is not lost, but in a real system, there are inefficiencies where energy is not completely converted to work, so while you may extract, say 100 J of energy, it might only do 90 J of work.