stars such as our sun
Catalysts speed a reaction that would naturally happen. Water does not spontaneously decompose into hydrogen and oxygen - it needs energy input to split. There is no catalyst that can change these facts.
The flask might feel cool to the touch as the reactants absorb heat conducted through the flask from your body. (This assumes that the reaction is happening at temperatures below your body temperature.)
Temperature affects the reactions occurring in a voltaic cell by increasing or decreasing the rate of reaction. Generally, an increase in temperature increases the rate of reaction because the molecules have more kinetic energy and collide more frequently. However, extreme temperatures can also lead to changes in the cell's performance and efficiency.
The double displacement reaction is not related to hydrogen bonding.
In homogenous reaction all the components/reactants taking part in the reaction form one single phase, with the reaction occurring in the bulk of this system. In heterogeneous reaction all the components/reactants taking part in the reaction are in different phases, with the reaction occurring between the delimiting surface of the components/reactants.
A large amount of energy. This naturally occurring reaction happens inside all stars and is called fusion.
nuclear fission
Light emitted from living organism as a result of naturally occurring chemical reaction inside the organism.
Nuclear fusion occurs naturally in the hearts of stars. To a lesser extent, it can happen in very massive planets (more than, say, 13 times the mass of Jupiter), where temperatures and pressures in the core are sufficient to cause hydrogen and deuterium to fuse.
It can be found naturally occurring in crude oil but is usually manufactured in large amounts when benzene and ethylene are combined in an acid-catylized chemical reaction.
Catalysts speed a reaction that would naturally happen. Water does not spontaneously decompose into hydrogen and oxygen - it needs energy input to split. There is no catalyst that can change these facts.
reversible reaction
Hydrogen-1 is fused into helium-4. This happens at high temperatures - somewhere around 14 million kelvin (which, at such high temperatures, is the same as 14 million degrees Celsius, for all practical purposes). There are two main reaction chains that in stars: the proton-proton chain reaction, and the CNO cycle. I suggest you read the corresponding Wikipedia articles, if you want more details about each of the reaction chains. Anyway, in our Sun, the predominant reaction chain is the proton-proton chain reaction.
The flask might feel cool to the touch as the reactants absorb heat conducted through the flask from your body. (This assumes that the reaction is happening at temperatures below your body temperature.)
No. If anything, a combustion reaction will consume hydrogen.
Hydrogen is an element, not a reaction. However, it is very combustible.
Temperature affects the reactions occurring in a voltaic cell by increasing or decreasing the rate of reaction. Generally, an increase in temperature increases the rate of reaction because the molecules have more kinetic energy and collide more frequently. However, extreme temperatures can also lead to changes in the cell's performance and efficiency.