How much heat is given off when 10 grams of water are cooled from 50°C to 40°C?

2 Answers
Oct 12, 2016

0.396 BTU

Explanation:

Convert 10 grams to pounds:
10 * 0.0022 = 0.022 pound

Convert 50 degrees C to Fahrenheit:
(50 * 9 / 5) + 32 = 122 degrees Fahrenheit

Convert 40 degrees C to Fahrenheit:
(40 * 9/5) + 32 = 104 degrees Fahrenheit

Calculate the change in temperature:
122 - 104 = 18 degrees Fahrenheit

Heat lost in British Thermal Units (BTU):
0.022 * 18 = 0.396 BTU

Oct 13, 2016

The process will give off 420 J of heat.

Explanation:

The energy q required to heat an object is given by the formula

color(blue)(bar(ul(|color(white)(a/a)q = mcΔTcolor(white)(a/a)|)))" "

where

m is the mass
c is the specific heat capacity
ΔT is the change in temperature

In your problem,

m = "10 g"
c = "4.184 J·K"^"-1""g"^"-1"
ΔT = T_"f" - T_"i" = "40 °C - 50 °C = -10 °C"

q = "10" color(red)(cancel(color(black)("g"))) × "4.184 J"·color(red)(cancel(color(black)("K"^"-1""g"^"-1"))) × ("-10" color(red)(cancel(color(black)("°C")))) = "-420 J"

The negative sign tells you that energy is being given off.