Thermochemistry

q=mcAT

100

in q=mcAT, c stands for...

specific heat capacity

200

a sample of metal is cooled from 150 degrees celsius to 25 degrees celsius. This process is ______.

exothermic

300

A sample of gold (c = 0.129) has a mass of 75.23 grams. It's initial temperature is 25 degrees celsius and is heated to 102 degrees celsius. How much heat is required for this process? Final answer in sig figs with units.

747.26 J --> 750 J

400

A sample 50. gram of iron (c = 0.45) has an initial temperature of 25 degrees celsius and releases -3000J of heat. What is the sample's final temperature?

23.67 degrees celsius --> 24 degrees celsius

heat exchange

100

This method is used in a lab to find the identity of a metal by its specific heat capacity.

calorimetry

200

when hot metal is placed in water that is in a calorimeter, what happens to the energy in the system?

energy is transferred to the water and the system reaches a thermal equilibrium

300

an unknown metal with a mass of 10.0 g is heated to 100.°C. The metal is placed in 25.0mL of water that is at 28°C. The final temperature of the system is 31°C. What is the specific heat of the metal? (c_water = 4.184)

0.454 J/g°C  --> 4.5x10^-1J/g°C

400

A 4.5g sample of copper at 120.°C  is cooled to 29°C  when placed in water at a temperature of 25°C. What was the mass of the water? (c_copper = 0.385 J/g°C, c_water = 4.184 J/g°C)

9.4 grams --> 9.4x10⁰ grams

latent heat

100

what is latent heat?

heat (energy) absorbed or released during a phase change, the energy required for a phase change to occur

200

Describe the energy changes when ice melts and then vaporizes.

energy is absorbed during melting and boiling to overcome forces between molecules in order to change phase

300

Ice (10. grams) at a temperature of -4°C melts to a final temperature of 25°C. How much energy is required for this process? Is it endothermic or exothermic?

c_ice = 2.03J/g°C , c_water = 4.184J/g°C , c_steam = 2.02J/g°C 

H_f = 334 J/g, H_v = 2260 J/g

4467.2 J

endothermic

400

Steam (15 grams) at a temperature of 120.°C is cooled to 99°C and condensed into water. How much energy is required for this process?

c_ice = 2.03J/g°C , c_water = 4.184J/g°C , c_steam = 2.02J/g°C 

H_f = 334 J/g, H_v = 2260 J/g

-34598.76 J

enthalpy

100

If the change in enthalpy is negative, what type of process is that?

exothermic (energy is released)

200

calculate ΔH for a reaction where H(products) = -300 kJ and H(reactants) = -500 kJ

200 kJ

300

Find the change in enthalpy for: CH₄(g)+2O₂(g)→CO₂(g)+2H₂O(l) 

Using the provided reactions:

H₂(g)+(1/2)O₂(g) → H₂O(l)     ΔH=−285.8kJ

C(s)+O₂(g) → CO₂(g)     ΔH=−393.5 kJ

C(s)+H₂(g) → CH₄(g)     ΔH=−74.8 kJ

-890.3 kJ

400

Calculate the change in enthalpy using the reaction:

CH₄ + Cl₂ → CH₃Cl + HCl

C-H: 412 kJ/mol

Cl-Cl: 243 412 kJ/mol

C-Cl: 338 412 kJ/mol

H-Cl: 431412 kJ/mol

-114 kJ/mol