function dydt = conhp(t, y, gas, mw)
    %% ODE system for a constant-pressure, adiabatic reactor
    %
    % Function ``CONHP`` evaluates the system of ordinary differential equations
    % for an adiabatic, constant-pressure, zero-dimensional reactor.
    % It assumes that the ``gas`` object represents a reacting ideal gas mixture.

    % Set the state of the gas, based on the current solution vector.
    gas.Y = y(2:end);
    gas.TP = {y(1), gas.P};
    nsp = gas.nSpecies;

    % energy equation
    wdot = gas.netProdRates;
    H = gas.enthalpies_RT';
    gas.basis = 'mass';
    tdot =- gas.T * GasConstant / (gas.D * gas.cp) .* wdot * H;

    % set up column vector for dydt
    dydt = [tdot
            zeros(nsp, 1)];

    % species equations
    rrho = 1.0 / gas.D;

    for i = 1:nsp
        dydt(i + 1) = rrho * mw(i) * wdot(i);
    end

end