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

2 Answers
John P
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

Ernest Z.
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.

Related questions
See all questions in Calorimetry
Impact of this question
11922 views around the world
You can reuse this answer
Creative Commons License