- positive q = system has gained heat from the surroundings (endothermic)

- negative q = system has released heat to the surroundings (exothermic)

- specific heat = measure the change in temperature that a known mass undergoes as it loses or gains a specific quantity of heat

Formulas to know:

q = m^{.}C^{.}∆T and q_{lost}= q_{gained}which means, m_{lost}^{.}C_{lost}^{.}∆T_{lost}= m_{gained}^{.}C_{gained}^{.}∆T_{gained}

∆T means a change in temperature represented by taking the final temperature minus the initial temperature.

Mass = 95.4 grams

Heat = 849 J

Initial Temperature = 25.0ºC

Final Temperature = 48.0ºC

Specific Heat (C) = ?

849 J = (95.4 grams) (C) (48.0ºC - 25.0ºC)

849 J = (95.4 grams) (C) (23ºC)

849 J = 2194.2 C

849 J/2194.2 = 2194.2/2194.2 C

C = 0.387 J/gºC

m

(50 grams) (4.184 J/gºC) (89ºC - x) = (25 grams) (4.184 J/gºC) (x - 23ºC)

(209.2) (89ºC - x) = (104.6) (x - 23ºC)

18618.8 - 209.2x = 104.6x - 2405.8

18618.8 + 2405.8 = 104.6x + 209.2x

21024.6 = 313.8x

21024.6/313.8 = 313.8/313.8 x

x = 67ºC

Calculate the amount of heat is required to raise the temperature of 50 grams of ice at -10ºC to steam at 120ºC.

Heat of fusion = 334 J/g

Heat of vaporization = 2260 J/g

specific heat of water = 4.184 J/gºC

specific heat of ice = 2.1 J/gºC

specific heat of steam = 1.7 J/gºC

1. Must raise the temperature to ice at 0ºC

2. Change the state from solid to liquid.

3. Raise the temperature from liquid at 0ºC to 100ºC.

4. Change the state from a liquid to a gas.

5. Raise the temperature from gas at 100ºC to 120ºC.

Raise the temperature → q = m•C•∆T

Change the state → Energy transferred = m•H

1. q = (50 g)(2.1 J/gºC)(0ºC -

2. e.t. = (50 g)(334 J/g) = 16,700 J

3. q = (50 g)(4.184 J/gºC)(100ºC - 0ºC) = 20,920 J

4. e.t. = (50 g)(2260 J/g) = 113,000 J

5. q = (50 g)(1.7 J/gºC)(120ºC - 100ºC) = 1,700 J

Total energy = the sum of all the energy = 153,370 J

Hess's Law

The idea behind Hess's law is illustrated as follows:

Reaction equation (1) with ∆H