Page 15 - Surviving Chemistry BFF Homework Helper and Test Prep Preview

A form of energy that flows from high to low
temperature areas.
heat
o
o
15 C 10 C

Calories (cal) and Joules (J) are units for heat.

Convert 5 calories to Joules. Convert 120 J to calories.

4.18 J X 1 cal
5 cal x --------- setup ------- = -------

1 cal = 4.18 J 1 cal 120 J 4.18 J

20.9 J calculated result X(4.18) = (120 cal)(1)

X = 28.7 cal

Heat to change a unit mass (m) of a substance by

onekelvin. (C for water is 4.18 J/g.K)

How much heat is required to change a 2.5 g sample

o o

q = mC of water from 38 C to 53 C?

q = (2.5)(4.18)(15) numerical setup

Use for calculating heat with a q = 156.8 J calculated result
)
temperature change (

Heat to change a unit mass of a solid to liquid at a

constant temperature. (Hf is 334 J/g for water).

q = mHf . How much heat must be released to freeze an 18 g

sample of water at 0 C?
o

Use for calculating heat during
q = (18)(334) numerical setup
solid-liquid phase change

q = 6012 J calculated result

Heat to change a unit mass of a liquid to vapor at a
constant temperature. (Hv is 2260 J/g for water).

What is the heat of vaporization of a liquid if a 20 g
q = mHv
sample requires 33,000 joules of energy to vaporize?

Use for calculating heat during
q 33000 J
liquid-gas phase change Hv = ---- = --------- numerical setup
Table B – heat constants m 20 g
for water
Hv = 1650 J/g calculated result
Table T – heat equations
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