11/1/22 - Heat During Reactions Flashcards
What is heat capacity?
The amount of heat needed to change the temperature of a substance by 1 K.
What is specific heat capacity?
The amount of heat needed to change the temperature of 1 gram of a substance by 1 K.
What is the equation for heat (q) lost or gained when given specific heat capacity (c), mass (m), and temperature change (ΔT)?
q = cmΔT
What are the units of specific heat capacity?
Joules/Kelvin
The specific heat capacity of water is 10.8 times higher than that of copper. How does this affect the amount of heat needed to raise the temperature of water?
It takes 10.8 times more heat to raise the temperature of an equal mass of water by the same magnitude.
When does ΔH = ΔE?
Change in enthalpy equals change in energy when pressure and volume are constant.
When does the change in enthalpy equal the change in heat?
When pressure is constant.
In pressure-volume work, a system’s volume changes due to pressure. Without any pressure, the volume is constant.
ΔH = ΔE + PΔV means “Enthalpy change = heat change + work change.” When ΔV = 0, ΔH = ΔE, leaving only heat change.
Why does enthalpy change (ΔH) equal energy change (ΔE) in most reactions?
Most energy is transferred as heat rather than work.
Is ΔH positive or negative for endothermic reactions?
Positive because heat is absorbed.
Is ΔH positive or negative for exothermic reactions?
Negative because heat is released.
What is calorimetry used for?
Measuring the heat transferred to or from a substance in a chemical reaction.
What are the two types of calorimetry?
Constant pressure (coffee cup) and constant volume (bomb)
