● Chemical compounds undergo `color{brown}("two types")` of changes.

● A physical change simply refers to a change in shape without `color{violet}("breaking of bonds")`.

● This is a `color{brown}("physical process.")`

● Another physical process is a change in state of matter: when ice melts into water, or when water becomes a `color{violet}("vapour.")`

● These are `color{brown}("physical processes.")`

● However, when `color{violet}("bonds")` are broken and new bonds are formed `color{violet}("during transformation")`, this will be called a `color{brown}("chemical reaction.")`

● For example : `Ba(OH)_2 + H_2SO_4 →BaSO_4 + 2H_2O`

● It is an `color{brown}("inorganic")` chemical reaction.

● Similarly, `color{violet}("hydrolysis of starch")` into glucose is an `color{brown}("organic")` chemical reaction.

● `color{violet}("Rate of a physical or chemical process")` refers to the amount of product formed per unit time.

It can be expressed as:

`"rate" = (deltaP)/(delta t)`

● Rate can also be called `color{brown}("velocity")` if the direction is specified.

● `color{violet}("Rates of physical and chemical processes")` are influenced by `color{brown}("temperature")` among other factors.

● A general rule of thumb is that rate doubles or decreases by half for every `color{brown}("10°C change")` in either direction.

● `color{violet}("Catalysed reactions")` proceed at rates vastly higher than that of `color{violet}("uncatalysed ones.")`

● When `color{violet}("enzyme catalyzed reactions")` are observed, the rate would be vastly higher than the same but `color{violet}("uncatalysed reaction.")`

● For example

`underset("carbondioxide ")(CO_2) + underset("water")(H_2O) overset("carbonic anhydrase")→ underset(" carbonic acid
")(H_2CO_3)`

● In the absence of any `color{violet}("enzyme this reaction")` is `color{brown}("very slow,")` with about 200 molecules of `H_2CO_3` being formed in an hour.

● However, by using the `color{violet}("enzyme")` present within the cytoplasm called `color{brown}("carbonic anhydrase")`, the reaction speeds dramatically with about `color{violet}("600,000 molecules")` being formed every second.

● The `color{violet}("enzyme")` has accelerated the reaction rate by about `color{violet}("10 million times.")`

● There are thousands of types of enzymes each `color{violet}("catalysing a unique chemical")` or `color{violet}("metabolic reaction.")`

● A `color{violet}("multistep chemical reaction")`, when each of the steps is catalysed by the same `color{violet}("enzyme complex")` or different enzymes, is called a `color{brown}("metabolic pathway.")`

● For example, `color{violet}("Glucose →2 Pyruvic acid")`

● `color{violet}(C_6H_(12)O_6 + O_2 →2C_3H_4 O_3 + 2H_2O)` is actually a `color{violet}("metabolic pathway")` in which glucose becomes `color{violet}("pyruvic acid")` through ten different enzyme catalysed `color{violet}("metabolic reactions")`.

● At this stage you should know that this very `color{violet}("metabolic pathway")` with one or two additional reactions gives rise to a variety of `color{violet}("metabolic end products.")`

● In our skeletal muscle, under anaerobic conditions, `color{brown}("lactic acid")` is formed.

● Under normal aerobic conditions, `color{brown}("pyruvic acid")` is formed.

● In yeast, during `color{brown}("fermentation,")` the same pathway leads to the `color{violet}("production of ethanol (alcohol).")`

● Hence, in different conditions different products are possible.