"a general rule of thumb is that rate doubles or decreases by half at every 100C change in either direction."what does direction mean here???

Let us consider a reaction
A + B <----> C + D - Energy

The reaction in the forward direction requires heat energy and on increasing temperature the reaction moves in the forward direction and for this the rate increases for every 10 0C by double the quantity. Whereas the backward direction is favoured by decrease of temperature and the reaction rate decreases by the same quantity for every 10 0C. 

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