Emotions and Freewill. I am under the impression that emotions are explained as sensations caused by mixtures of hormones or electrical pulses to reactions of events, whilst freewill is explained by the intelligent nature of humans, unlike animals, who are unintelligent and thus have no free will.
I do not really think monism is put forth as any kind of detailed or scientific explanation for emotions or for free will. In general the various forms of monism (and there are many) are contrasted with Descartes type dualism (mind and matter as separate substances which interact through some mysterious or divine intervention).
Materialism can be thought of as a form of monism in which the primary stuff of which reality is made is matter (or in physicalism, physical forces) and ultimately mind and subjective experience are explainable in physical or material terms.
Idealism is another form of monism in which the primary stuff of which reality is made is really mental experience. In the age of science which provides explanations in material or physical terms, materialism or physicalism is much more prevalent than idealism.
I presume you are referring more to so called neutral monisms in which the primary constituents of reality are held to be something other than either primarily just mental experiences or material substances.
I am for example a particular kind of neutral monist. I support a form of process philosophy in the manner of A.N.Whitehead. In this view the primary elements or stuff of which reality is made are neither material nor mental. Reality is reality composed of events or moments of experience. This is often referred to as a view which emphasizes change, flux, impermanence, process (becoming) over any kind of enduring static (being) or substance. In process philosophy events are the primary stuff of reality and all events have both material and mental aspects. Moments or droplets of experience or events sequentially follow one another (perpetual perishing and rebirth). Each new moment of experience incorporates elements of the past (through a form of non sensory perception called prehension) and also incorporates possibilities from the future (the actualization of primordial ideals in a process of concrescence). All events have some degree of indeterminism, creativity, freedom or novelty (choose your term). All events have both a mental (perceptual, interiority, subjective, indeterminate) aspect and a material (physical) aspect.
For a process philosopher the material and the mental are fused in events. One should not confuse the term mental in process philosophy with human type consciousness. Human type consciousness is the result of highly complex and integrated experience based on more prevalent and widespread primitive mental properties which are pervasive in nature (perception, memory, interiority). The stable material objects of perception (for process thinkers) are repetitive events and mostly represent aggregates with little complex integration or interior structure. Becoming (process, events) is primary reality not stable objects (being, matter). Aggregates have no complex mental properties although the individual constituents of matter do have primitive mental properties (panpsychism). Time is merely the sequencing of events. Complex mental events are merely the combination of more primitive mental properties into highly ordered, complex and integrated societies or organisms. The mental does not so much mysteriously emerge from primary insensate inert matter as combine in moments of integrated complex experience.
Anyway when one asks about free will and emotions in combination with monism, this is the picture of the process philosophy type of monism. This is not a scientific theory since science is limited to the external observable physical properties of reality. Science can not get at the subjective, interior mental or experiential side of reality. It is a philosophical position. One that in my view deserves more serious consideration than the dominant mechanistic materialistic deterministic Newtonian (world as machine) worldview gives it. The world is engaged in a continuous process of creative advance into novelty. The world is more like a perceptive, living enchanted organism than like an inert dead mechanical machine. For people with this view, time, emotions, free will and subjective experience are not quite so miraculously emergent or rare as for those who think the primary elements of reality are inert, dead insensate bits of matter knocked about like solid little billiard balls by blind, purposeless physical forces. There is nothing about the process view which is directly incompatible with science especially modern physics and of course process philosophy is also compatible with certain forms of process theology.