Answer:
A. to determine the efficiency of the reaction
Explanation:
- Percentage is the ratio of the actual yield to theoretical yield as a percentage. It is calculated by dividing the actual yield by theoretical yield then multiplying by 100%.
- Calculation of percentage yield is important as it helps in the determination of efficiency of a reaction. For example in most industries for the purpose of making the most product with the least waste.
- Additionally, calculating the percentage yield helps in determining other products that may be formed during the reactions.
Answer:
Equilibrium constant is 0.4
Explanation:
We propose the equilibrium:
PCl₅(g) ⇄ PCl₃(g) + Cl₂(g)
Initially 0.72 mol
We have the 0.72 moles of the PCl₅.
React x x x
X amount has reacted, so in the equilibrium we have:
0.72 - x 0.4 0.4
If we initially have 0.72 moles and we have 0.4 moles at the equilibrium, it means that 0.3 moles has been reacted.
Let's make the expression for Kc:
Kc = [PCl₃] . [Cl₂] / [PCl₅]
Kc = 0.4 . 0.4 / 0.4
Kc = 0.4
The correct answer is:
b: Heluim
Explanation:
The caffeine contains:
carbon , nitrogen , oxygen ,
hydrogen.
Caffeine is a primary nervous system energizer of the methylxanthine class. It is the world's most universally consumed psychoactive drug. Unlike many other psychoactive elements, it is fair and unlimited in nearly all parts of the world. Caffeine can be arranged as an alkaloid, a term used for substances originated as end results of nitrogen metabolism in some plants.
Answer is (D) - It is exothermic and will have a negative enthalpy.
If the reactants are at a higher potential energy compared to the products, it means reactants have more energy than the products. That energy is released to the environment as heat. Due to the releasing of heat to the surrounding, the reaction is exothermic. Since the reaction is exothermic; the enthalpy of the reaction will be negative value.
Answer:
Heat change is -14,175 joules, Exothermic
Explanation:
We are given;
- Mass of aluminium bar as 350.0 g
- initial temperature as 70.0 °C
- Final temperature as 25 °C
We are required to determine the heat change and indicate whether endothermic or exothermic;
We know that;
Heat change = Mass of a substance × specific heat × change in temperature
In this case;
Mass of Aluminium = 350.0 g
Change in temperature = (25 - 70)
= -45° C
Specific heat of aluminium = 0.90 J/g°C
Therefore;
Heat change = 350.0 g × 0.90 J/g°C × -45°C
=-14,175 joules
The heat change is exothermic because it is a negative value, also because cooling process involves heat loss and thus an exothermic reaction.
