6. A 35-g glass thermometer reads 21.6°C before it is placed in 135 mL of water. When the water and thermometer come to equilibrium, the thermometer reads 39.2°C. What was the original temperature of the water?
The specific heats are as follows: cwater= 4186 J kg^-1 °C^-1 and cglass = 840 J kg^-1 °C^-1

Question

6. A 35-g glass thermometer reads 21.6°C before it is placed in 135 mL of water. When the water and thermometer come to equilibrium, the thermometer reads 39.2°C. What was the original temperature of the water?
The specific heats are as follows: cwater= 4186 J kg^-1 °C^-1 and cglass = 840 J kg^-1 °C^-1

deoxna · Answer

How can I figure out the mass of the water (needed for the calculation) if I don't know the temperature?

I'm using the relation
Q1=−Q2
and Q=mcT

anonymous · Answer

use Azaz Black..., you know?

deoxna · Answer

No.....

anonymous · Answer

Qglass = Qwater
mg. cg. dTg = mw. cw. dTw
mg . cg. (Tmix - Tglass) = (rho x volume of water). cw. (Twater - Tmix)

mg is mass of glass, cg is specific Qalor of glass, cw is spesific Qalor of water..,
so., you can find out of the original temperature of the water..,

anonymous · Answer

Tmix or T at the equilibrium is 39.2 C in the question...,

deoxna · Answer

Yes, but what's rho?

anonymous · Answer

rho is the density of the water

deoxna · Answer

But doesn't the density also depend on the temperature?

deoxna · Answer

I understand it maybe negligible for the temperatures water is liquid at one atmosphere, but still. Theoretically, wouldn't it depend on temperature?

anonymous · Answer

Yes but little changes

deoxna · Answer

Ok thanks!

anonymous · Answer

ok ur welcome.., this figure for you., check this out

deoxna · Answer

Thank you again. I also just found out that a kilogram is defined as the mass of 1 liter of water at 4ºC. Hence 16 L is about 16 kg of water at just about any temperature (your table above shows the difference is practically negligible).

anonymous · Answer

yes of course.., two thumbs for you