A system is a part of the <em>physical</em> universe defined <em>arbitrarily</em> for observation purposes.
Boundaries are a part of the <em>physical</em> universe that are around the system.
In a scientific sense, a system is a part of the <em>physical</em> universe whose boundaries, that is, the limit between the system and its surroundings, are defined <em>arbitrarily</em> for observation purposes.
A system contains at least a model, represented in a phenomenological way, and it can be isolated (no mass nor energy interactions), closed (no mass interactions) or open.
The surroundings are a part of the <em>physical</em> universe that are around the system.
An example is a coffee-maker, where coffee-maker the system and air represents the surroundings, the coffee-maker receives energy from a heat source to warm up itself and releases part of such energy to the air.
We kindly invite to check this question on systems and surroundings: brainly.com/question/6044762
The mass of sulfur in the sample is 0.31g
To calculate mass of sulfur in sample: given that amount galena is 2.34g and mass of lead is 2.03 g as galena contain both lead and sulfur the mass of sulfur = mass of galena- mass of lead , that is, 2.34- 2.03=0.31g.The molecular mass is a algebraic sum of atomic mass of each element in the compound thus the mass of the compound can be obtained by adding atomic of each element. Lead(II) sulphide occurs naturally as the mineral galena, often known as lead glance (PbS). It is a significant source of silver and the most significant lead ore.
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The boiling point of a liquid can be raised by adding pressure. Like wise, if you lower the pressure the boiling point goes down. This can be explained by the fact that boiling occurse when the vapor pressure equals the outside pressure so when the outside pressure rises the vapor pressure required for boiling also rises. Vapor pressure is proportional to temperature and therefore temperature needs to increase to make the vapor pressure increase.
I hope this helps. Let me know in the comments if anything is unclear or if you want me to explain anything further.