10/28/22 - Heat, Work, and Enthalpy Flashcards
What is the equation for change in energy?
ΔE = q + w (heat + work)
In ΔE = q + w, when is heat (q) positive?
When the system increases in temperature, gaining heat.
In ΔE = q + w, when is work (w) positive?
When work is done on the system, causing it to absorb energy.
In ΔE = q + w, when is work (w) negative?
When the system does work, causing it to release energy to the surroundings.
What is an endothermic reaction?
One in which a system absorbs energy.
What is an exothermic reaction?
One in which a system releases energy.
What is pressure-volume work?
Work done when a system’s volume changes in the presence of external pressure.
What is the equation for pressure-volume work?
w = -PΔV
Does a system gain or lose internal energy when it contracts in volume?
It gains internal energy. The surroundings do work on the system to contract it, and the system gains energy as work.
When a system increases in volume, it loses energy.
What is enthalpy?
Internal energy plus the product of pressure and volume.
What is the equation for enthalpy (H)?
H = E + PV
What is the equation for a change in enthalpy (H)?
ΔH = ΔE + PΔV
