Question about Q=mcΔT when doing calorimetry

In summary, when solving calorimetry problems using the equation Q=mcΔT, the 'm' refers to the mass of the substance being tested, not the sum of the mass of the substance and the mass of water. This is because 'c' is specific heat, which is defined as the energy required to raise the temperature of one unit mass of the substance by one degree. Therefore, 'm' in the equation represents the mass of the substance only.
  • #1
deezer
18
0

Homework Statement



When using the equation Q=mcΔT for the substance being tested is it the mass of the substance or the mass of the substance + mass of water.

Homework Equations





The Attempt at a Solution



So when I solve calorimetry problems, I usually find Qwater. Then I set Qsubstance=-Qwater. But then I have to use mcΔT, I'm not sure if it's the mass of the substance or the mass of the substance + mass of the water because I've gotten a few questions wrong and the textbook briefly mentioned the sum of masses but gave no examples. Thanks for your input.
 
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  • #2
Re-arrange your equation as follows:

c = [itex]\frac{Q}{mΔT}[/itex]

Since 'c' is for the substance, what would 'm' be for?
 
  • #3
m is for the substance right? Not the sum of the mass of the water and substance.
 
  • #4
deezer said:
m is for the substance right? Not the sum of the mass of the water and substance.
Yes, and you can relate to the definition of specific heat: energy required to raise the temperature of one unit mass of the 'substance' on unit degree.
 
  • #5
edgepflow said:
Yes, and you can relate to the definition of specific heat: energy required to raise the temperature of one unit mass of the 'substance' on unit degree.

Like specific heat of brine :tongue:
 

1. What does the equation Q=mcΔT represent in calorimetry?

In calorimetry, the equation Q=mcΔT represents the amount of heat gained or lost by a substance during a change in temperature. Q is the heat, m is the mass of the substance, c is the specific heat capacity of the substance, and ΔT is the change in temperature.

2. Why is Q=mcΔT important in calorimetry?

Q=mcΔT is important in calorimetry because it allows us to calculate the amount of heat transferred during a temperature change, which is a crucial aspect of understanding the thermal properties of a substance. It helps us determine the specific heat capacity of a substance, which is useful in various fields such as engineering and chemistry.

3. How is the Q=mcΔT equation used in calorimetry experiments?

In calorimetry experiments, the Q=mcΔT equation is used to calculate the heat gained or lost by a substance, by measuring its change in temperature. This is done by measuring the mass of the substance, determining its specific heat capacity, and measuring the change in temperature. These values are then plugged into the equation to calculate the heat.

4. Can Q=mcΔT be applied to all substances?

While Q=mcΔT is a commonly used equation in calorimetry, it is not applicable to all substances. This equation is based on the assumption that the specific heat capacity of a substance remains constant throughout the temperature change. However, for some substances, such as those undergoing a phase change, the specific heat capacity may vary. In these cases, a modified equation or approach may be necessary.

5. What are the units for Q=mcΔT?

The units for Q=mcΔT will depend on the units used for the mass, specific heat capacity, and temperature change. Generally, the mass will be measured in grams or kilograms, the specific heat capacity in joules per gram per degree Celsius (J/g°C) or joules per kilogram per degree Celsius (J/kg°C), and the temperature change in degrees Celsius (°C) or Kelvin (K). Therefore, the units for Q will be joules (J) or kilojoules (kJ).

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