If the decomposition of hydrogen peroxide into water and oxygen gas is an exothermic reaction, we would expect the final temperature to be lower than the initial temperature of 28˚C.
This is because during an exothermic reaction, energy is released from the system into the surroundings in the form of heat. In other words, the energy of the products (water and oxygen) is lower than the energy of the reactants (hydrogen peroxide), and the excess energy is released into the surroundings.
As a result, the temperature of the surroundings (in this case, the container holding the reaction) will increase, while the temperature of the system (the reactants and products) will decrease. This means that the final temperature of the reaction will be lower than the initial temperature of 28˚C.
Overall, we would expect the reaction to release heat into the surroundings, causing the temperature of the surroundings to increase while the temperature of the system decreases.