# reaction 2

• Feb 14th 2010, 02:24 PM
william
reaction 2
1.05 g MgO is added to 110.5ml HCL with an initial temperature of 21.5 degrees Celsius and a final temperature of 34.5 degrees Celsius. calculate the KJ of energy released for the reaction. assume that 4.18 J of energy is required to change the temperature of one mL of solution to one Celsius degree.

i am assuming we must use q=mcdeltat, although i keep getting stuck
• Feb 16th 2010, 10:03 AM
earboth
Quote:

Originally Posted by william
1.05 g MgO is added to 110.5ml HCL with an initial temperature of 21.5 degrees Celsius and a final temperature of 34.5 degrees Celsius. calculate the KJ of energy released for the reaction. assume that 4.18 J of energy is required to change the temperature of one mL of solution to one Celsius degree.

i am assuming we must use q=mcdeltat, although i keep getting stuck

1. From $\displaystyle c=4.18\ \frac{kJ}{kg \cdot K}$ it seems that you are refering to water.

2. You have to convert the measurements into kg:

1.05 g = 0.00105 kg
110.5 ml HCl (nearly water!) = 0.1105 kg
difference of temperature (measured in Kelvin) 34.5°C - 21.5°C = 13 K

3. Now use the mentioned formula to calculate the energy:

$\displaystyle Q = m \cdot c \cdot \Delta t$

That means:

$\displaystyle Q = 0.11155\ kg \cdot 4.18\ \frac{kJ}{kg \cdot K} \cdot 13\ K$