1. What mass of methane must be burned in order to liberate 11,524 kJ of heat? 2. A sample of Ammonia (NH3) liberates 4.94 kJ as it solidifies at its melting point. What is the mass of the sample?

3. A cooking gas cylinder is assumed to contain 6.7 kg of fuel gas (molar mass 58 g/mol). The heat of combustion of fuel gas is 2465 kJ/mol. A family needs 8 x 103 kJ of energy per day of cooking. Then how long would cylinder will last (approx.)? (Assume 29% of gas goes waste due to incomplete combustion).

4. How much heat is required to warm 142 g of ice from -40.0o C to 0.0o C, melt the ice. warm the water from 0.0o C to 100.0o C, boil the water, and heat the steam to 173.0o C?

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.

definition

                    entropy is a measure of the randomness or the extent of disorder of a chemical process.

                      enthalpy is a measure of the heat change of a reaction occurring at a constant pressure.

measurement units:

                        entropy is measured in joule per kelvin (jk⁻¹)   whereas enthalpy is measured in joule per mole (jmol⁻¹)

requirements:

                            entropy has no requirements or limits, and its change is measured by the division between the heat change of the chemical process and the temperature.

                              in contrast, enthalpy can only be related to the heat change of the reaction under standard conditions.

colorless gas, exhibiting a blue glow when placed in an electric field

b) solid

its a type of rock

substituting a hydrogen atom with a halogen in a hydrocarbon:

- the single bond remains single. a is wrong.

- the bond with hydrogen is as strong as with a halogen. c is wrong

- a hydrocarbon is saturated if there is no double bond. we do not know that so d is wrong.

- carbon will always have four valence electrons. e is wrong.

by elimination, the correct answer is b. the boiling point of the new compound increases.